diff --git a/Check/CustomErrorPages.php b/Check/CustomErrorPages.php
index 799b102d..8ca2b5d4 100644
--- a/Check/CustomErrorPages.php
+++ b/Check/CustomErrorPages.php
@@ -4,6 +4,7 @@
 
 use Laminas\Diagnostics\Check\CheckInterface;
 use Laminas\Diagnostics\Result\Failure;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 
 /**
@@ -35,6 +36,9 @@ public function __construct(array $errorCodes, $path, $projectDir)
         $this->projectDir = $projectDir;
     }
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $dir = $this->getCustomTemplateDirectory();
@@ -55,15 +59,15 @@ public function check()
         return new Success();
     }
 
+    /**
+     * @return string
+     */
     public function getLabel()
     {
         return 'Custom error pages';
     }
 
-    /**
-     * @return string
-     */
-    private function getCustomTemplateDirectory()
+    private function getCustomTemplateDirectory(): string
     {
         if ($this->projectDir !== $this->path) {
             return $this->path; // using custom directory
diff --git a/Check/DoctrineDbal.php b/Check/DoctrineDbal.php
index a096c052..f61144fc 100644
--- a/Check/DoctrineDbal.php
+++ b/Check/DoctrineDbal.php
@@ -4,6 +4,7 @@
 
 use Doctrine\Persistence\ConnectionRegistry;
 use Laminas\Diagnostics\Check\AbstractCheck;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 
 class DoctrineDbal extends AbstractCheck
@@ -17,6 +18,9 @@ public function __construct(ConnectionRegistry $registry, $connectionName = null
         $this->connectionName = $connectionName;
     }
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $connection = $this->manager->getConnection($this->connectionName);
diff --git a/Check/DoctrineDbalCollection.php b/Check/DoctrineDbalCollection.php
index cc29ea05..0b957883 100644
--- a/Check/DoctrineDbalCollection.php
+++ b/Check/DoctrineDbalCollection.php
@@ -26,6 +26,9 @@ public function __construct(ConnectionRegistry $manager, $connections)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/DoctrineMigrationsCollection.php b/Check/DoctrineMigrationsCollection.php
index f182d840..4fe2e572 100644
--- a/Check/DoctrineMigrationsCollection.php
+++ b/Check/DoctrineMigrationsCollection.php
@@ -48,6 +48,9 @@ public function __construct(
         $this->migrations = $migrations;
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         if (null === $this->checks) {
diff --git a/Check/DoctrineMongoDb.php b/Check/DoctrineMongoDb.php
index d85fab1b..39e6a51b 100644
--- a/Check/DoctrineMongoDb.php
+++ b/Check/DoctrineMongoDb.php
@@ -5,6 +5,7 @@
 use Doctrine\Bundle\MongoDBBundle\ManagerRegistry;
 use Laminas\Diagnostics\Check\AbstractCheck;
 use Laminas\Diagnostics\Result\Failure;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 use MongoDB\Driver\Command;
 use MongoDB\Driver\Exception\ConnectionException;
@@ -20,6 +21,9 @@ public function __construct(ManagerRegistry $registry, $connectionName = null)
         $this->connectionName = $connectionName;
     }
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $connection = $this->manager->getConnection($this->connectionName);
diff --git a/Check/DoctrineMongoDbCollection.php b/Check/DoctrineMongoDbCollection.php
index 1e9980c5..3fea5785 100644
--- a/Check/DoctrineMongoDbCollection.php
+++ b/Check/DoctrineMongoDbCollection.php
@@ -26,6 +26,9 @@ public function __construct(ConnectionRegistry $manager, $connections)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/Expression.php b/Check/Expression.php
index edaeb2cd..5fdac568 100644
--- a/Check/Expression.php
+++ b/Check/Expression.php
@@ -4,6 +4,7 @@
 
 use Laminas\Diagnostics\Check\CheckInterface;
 use Laminas\Diagnostics\Result\Failure;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 use Laminas\Diagnostics\Result\Warning;
 use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
@@ -36,6 +37,9 @@ public function __construct($label, $warningCheck = null, $criticalCheck = null,
         $this->criticalMessage = $criticalMessage;
     }
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $language = $this->getExpressionLanguage();
@@ -51,12 +55,15 @@ public function check()
         return new Success();
     }
 
+    /**
+     * @return string
+     */
     public function getLabel()
     {
         return $this->label;
     }
 
-    protected function getExpressionLanguage()
+    protected function getExpressionLanguage(): ExpressionLanguage
     {
         $language = new ExpressionLanguage();
         $language->register(
diff --git a/Check/ExpressionCollection.php b/Check/ExpressionCollection.php
index 2eded80c..84b4252f 100644
--- a/Check/ExpressionCollection.php
+++ b/Check/ExpressionCollection.php
@@ -24,6 +24,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/GuzzleHttpServiceCollection.php b/Check/GuzzleHttpServiceCollection.php
index 9cdab888..e5fc81ad 100644
--- a/Check/GuzzleHttpServiceCollection.php
+++ b/Check/GuzzleHttpServiceCollection.php
@@ -31,6 +31,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/HttpServiceCollection.php b/Check/HttpServiceCollection.php
index 514f120e..4facaf22 100644
--- a/Check/HttpServiceCollection.php
+++ b/Check/HttpServiceCollection.php
@@ -22,6 +22,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/MemcacheCollection.php b/Check/MemcacheCollection.php
index 88d3921d..33da0fc8 100644
--- a/Check/MemcacheCollection.php
+++ b/Check/MemcacheCollection.php
@@ -22,6 +22,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/MemcachedCollection.php b/Check/MemcachedCollection.php
index f48cf6be..bbd83feb 100644
--- a/Check/MemcachedCollection.php
+++ b/Check/MemcachedCollection.php
@@ -22,6 +22,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/PdoConnectionCollection.php b/Check/PdoConnectionCollection.php
index 55d913b0..a116806f 100644
--- a/Check/PdoConnectionCollection.php
+++ b/Check/PdoConnectionCollection.php
@@ -17,6 +17,9 @@ public function __construct(array $connections)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/PhpFlagsCollection.php b/Check/PhpFlagsCollection.php
index 1aae5941..c2c7f950 100644
--- a/Check/PhpFlagsCollection.php
+++ b/Check/PhpFlagsCollection.php
@@ -22,6 +22,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/PhpVersionCollection.php b/Check/PhpVersionCollection.php
index 110728cc..c6284483 100644
--- a/Check/PhpVersionCollection.php
+++ b/Check/PhpVersionCollection.php
@@ -22,6 +22,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/ProcessRunningCollection.php b/Check/ProcessRunningCollection.php
index 7543e3fc..e2462ed9 100644
--- a/Check/ProcessRunningCollection.php
+++ b/Check/ProcessRunningCollection.php
@@ -26,6 +26,9 @@ public function __construct($processes)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/RabbitMQCollection.php b/Check/RabbitMQCollection.php
index c4cb301c..13e73c76 100644
--- a/Check/RabbitMQCollection.php
+++ b/Check/RabbitMQCollection.php
@@ -36,6 +36,9 @@ public function __construct(array $configs)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/RedisCollection.php b/Check/RedisCollection.php
index d8a8fea4..78ae743c 100644
--- a/Check/RedisCollection.php
+++ b/Check/RedisCollection.php
@@ -26,7 +26,7 @@ public function __construct(array $configs)
         }
     }
 
-    private function parseDsn(array &$config)
+    private function parseDsn(array &$config): void
     {
         $config = \array_merge($config, \parse_url($config['dsn']));
 
@@ -45,6 +45,9 @@ private function parseDsn(array &$config)
         }
     }
 
+    /**
+     * @return array|\Traversable
+     */
     public function getChecks()
     {
         return $this->checks;
diff --git a/Check/SymfonyRequirements.php b/Check/SymfonyRequirements.php
index 623afb47..e53b7c91 100644
--- a/Check/SymfonyRequirements.php
+++ b/Check/SymfonyRequirements.php
@@ -4,6 +4,7 @@
 
 use Laminas\Diagnostics\Check\CheckInterface;
 use Laminas\Diagnostics\Result\Failure;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 use Laminas\Diagnostics\Result\Warning;
 
@@ -21,6 +22,9 @@ public function __construct($file)
         require $file;
     }
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $symfonyRequirements = new \SymfonyRequirements();
@@ -36,6 +40,9 @@ public function check()
         return new Success();
     }
 
+    /**
+     * @return string
+     */
     public function getLabel()
     {
         return 'Symfony2 Requirements';
diff --git a/Check/SymfonyVersion.php b/Check/SymfonyVersion.php
index c53e4872..ac7778d6 100644
--- a/Check/SymfonyVersion.php
+++ b/Check/SymfonyVersion.php
@@ -4,6 +4,7 @@
 
 use Laminas\Diagnostics\Check\CheckInterface;
 use Laminas\Diagnostics\Result\Failure;
+use Laminas\Diagnostics\Result\ResultInterface;
 use Laminas\Diagnostics\Result\Success;
 use Laminas\Diagnostics\Result\Warning;
 use Symfony\Component\HttpClient\HttpClient;
@@ -20,6 +21,9 @@ class SymfonyVersion implements CheckInterface
     const PACKAGIST_URL = 'https://packagist.org/packages/symfony/symfony.json';
     const VERSION_CHECK_URL = 'https://symfony.com/releases/%s.json';
 
+    /**
+     * @return ResultInterface
+     */
     public function check()
     {
         $currentBranch = Kernel::MAJOR_VERSION.'.'.Kernel::MINOR_VERSION;
@@ -47,6 +51,9 @@ public function check()
         return new Success(sprintf('Your current Symfony branch reaches it\'s end of life in %s.', $endOfLife));
     }
 
+    /**
+     * @return string
+     */
     public function getLabel()
     {
         return 'Symfony version';
@@ -55,11 +62,9 @@ public function getLabel()
     /**
      * @param string $branch
      *
-     * @return string
-     *
      * @throws \Exception
      */
-    private function getLatestVersion($branch)
+    private function getLatestVersion($branch): string
     {
         $response = $this->getResponseAndDecode(self::PACKAGIST_URL);
 
@@ -96,13 +101,11 @@ function ($value) use ($branch) {
     }
 
     /**
-     * @param $url
-     *
-     * @return array
+     * @param string $url
      *
      * @throws \Exception
      */
-    private function getResponseAndDecode($url)
+    private function getResponseAndDecode($url): array
     {
         if (class_exists(HttpClient::class)) {
             return HttpClient::create()->request('GET', $url)->toArray();
diff --git a/Command/HealthCheckCommand.php b/Command/HealthCheckCommand.php
index a3acf67d..fd33772c 100644
--- a/Command/HealthCheckCommand.php
+++ b/Command/HealthCheckCommand.php
@@ -26,7 +26,7 @@ public function __construct(ConsoleReporter $reporter, RawConsoleReporter $rawRe
         parent::__construct($name);
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName('monitor:health')
@@ -53,10 +53,7 @@ protected function configure()
         ;
     }
 
-    /**
-     * @return int
-     */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $failureCount = 0;
 
diff --git a/Command/ListChecksCommand.php b/Command/ListChecksCommand.php
index c4180bdc..63157bc7 100644
--- a/Command/ListChecksCommand.php
+++ b/Command/ListChecksCommand.php
@@ -22,7 +22,7 @@ public function __construct(RunnerManager $runnerManager, Runner $runner, $name
         parent::__construct($name);
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName('monitor:list')
@@ -34,7 +34,7 @@ protected function configure()
         ;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         switch (true) {
             case $input->getOption('reporters'):
@@ -54,7 +54,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         return 0;
     }
 
-    protected function listChecks(InputInterface $input, OutputInterface $output)
+    protected function listChecks(InputInterface $input, OutputInterface $output): void
     {
         $group = $input->getOption('group');
 
@@ -69,7 +69,7 @@ protected function listChecks(InputInterface $input, OutputInterface $output)
         $this->doListChecks($output, $runner);
     }
 
-    protected function listAllChecks(OutputInterface $output)
+    protected function listAllChecks(OutputInterface $output): void
     {
         foreach ($this->runnerManager->getRunners() as $group => $runner) {
             $output->writeln(sprintf('<fg=yellow;options=bold>%s</>', $group));
@@ -78,7 +78,7 @@ protected function listAllChecks(OutputInterface $output)
         }
     }
 
-    protected function listReporters(OutputInterface $output)
+    protected function listReporters(OutputInterface $output): void
     {
         $reporters = $this->runner->getAdditionalReporters();
         if (0 === count($reporters)) {
@@ -90,14 +90,14 @@ protected function listReporters(OutputInterface $output)
         }
     }
 
-    protected function listGroups(OutputInterface $output)
+    protected function listGroups(OutputInterface $output): void
     {
         foreach ($this->runnerManager->getGroups() as $group) {
             $output->writeln($group);
         }
     }
 
-    private function doListChecks(OutputInterface $output, Runner $runner)
+    private function doListChecks(OutputInterface $output, Runner $runner): void
     {
         $checks = $runner->getChecks();
 
diff --git a/Composer/ScriptHandler.php b/Composer/ScriptHandler.php
index 86759bde..808c3408 100644
--- a/Composer/ScriptHandler.php
+++ b/Composer/ScriptHandler.php
@@ -11,7 +11,7 @@
  */
 class ScriptHandler extends BaseHandler
 {
-    public static function checkHealth(Event $event)
+    public static function checkHealth(Event $event): void
     {
         $options = self::getOptions($event);
 
diff --git a/Controller/HealthCheckController.php b/Controller/HealthCheckController.php
index 9c9f4028..9a7cbe03 100644
--- a/Controller/HealthCheckController.php
+++ b/Controller/HealthCheckController.php
@@ -29,10 +29,7 @@ public function __construct(RunnerManager $runnerManager, PathHelper $pathHelper
         $this->failureStatusCode = $failureStatusCode;
     }
 
-    /**
-     * @return Response
-     */
-    public function indexAction(Request $request)
+    public function indexAction(Request $request): Response
     {
         $group = $this->getGroup($request);
 
@@ -61,10 +58,7 @@ public function indexAction(Request $request)
         return new Response($content, 200, ['Content-Type' => 'text/html']);
     }
 
-    /**
-     * @return Response
-     */
-    public function listAction(Request $request)
+    public function listAction(Request $request): JsonResponse
     {
         $ret = [];
 
@@ -77,10 +71,7 @@ public function listAction(Request $request)
         return new JsonResponse($ret);
     }
 
-    /**
-     * @return JsonResponse
-     */
-    public function listAllAction()
+    public function listAllAction(): JsonResponse
     {
         $allChecks = [];
 
@@ -93,20 +84,14 @@ public function listAllAction()
         return new JsonResponse($allChecks);
     }
 
-    /**
-     * @return JsonResponse
-     */
-    public function listGroupsAction()
+    public function listGroupsAction(): JsonResponse
     {
         $groups = $this->runnerManager->getGroups();
 
         return new JsonResponse($groups);
     }
 
-    /**
-     * @return Response
-     */
-    public function runAllChecksAction(Request $request)
+    public function runAllChecksAction(Request $request): JsonResponse
     {
         $report = $this->runTests($request);
 
@@ -116,10 +101,7 @@ public function runAllChecksAction(Request $request)
         ]);
     }
 
-    /**
-     * @return Response
-     */
-    public function runAllChecksHttpStatusAction(Request $request)
+    public function runAllChecksHttpStatusAction(Request $request): Response
     {
         $report = $this->runTests($request);
 
@@ -131,10 +113,8 @@ public function runAllChecksHttpStatusAction(Request $request)
 
     /**
      * @param string $checkId
-     *
-     * @return Response
      */
-    public function runSingleCheckHttpStatusAction($checkId, Request $request)
+    public function runSingleCheckHttpStatusAction($checkId, Request $request): Response
     {
         $report = $this->runTests($request, $checkId);
 
@@ -146,10 +126,8 @@ public function runSingleCheckHttpStatusAction($checkId, Request $request)
 
     /**
      * @param string $checkId
-     *
-     * @return Response
      */
-    public function runSingleCheckAction($checkId, Request $request)
+    public function runSingleCheckAction($checkId, Request $request): JsonResponse
     {
         $results = $this->runTests($request, $checkId)->getResults();
 
@@ -158,10 +136,8 @@ public function runSingleCheckAction($checkId, Request $request)
 
     /**
      * @param string|null $checkId
-     *
-     * @return ArrayReporter
      */
-    protected function runTests(Request $request, $checkId = null)
+    protected function runTests(Request $request, $checkId = null): ArrayReporter
     {
         $reporters = $request->query->get('reporters') ?? [];
 
@@ -181,11 +157,9 @@ protected function runTests(Request $request, $checkId = null)
     }
 
     /**
-     * @return Runner
-     *
      * @throws \Exception
      */
-    private function getRunner(Request $request)
+    private function getRunner(Request $request): Runner
     {
         $group = $this->getGroup($request);
 
@@ -198,18 +172,12 @@ private function getRunner(Request $request)
         throw new \RuntimeException(sprintf('Unknown check group "%s"', $group));
     }
 
-    /**
-     * @return string
-     */
-    private function getGroup(Request $request)
+    private function getGroup(Request $request): string
     {
         return $request->query->get('group') ?: $this->runnerManager->getDefaultGroup();
     }
 
-    /**
-     * @return Response
-     */
-    public function listReportersAction()
+    public function listReportersAction(): JsonResponse
     {
         return new JsonResponse($this->runnerManager->getReporters());
     }
diff --git a/DependencyInjection/Compiler/AddGroupsCompilerPass.php b/DependencyInjection/Compiler/AddGroupsCompilerPass.php
index a4ad8052..ffbceb72 100644
--- a/DependencyInjection/Compiler/AddGroupsCompilerPass.php
+++ b/DependencyInjection/Compiler/AddGroupsCompilerPass.php
@@ -9,7 +9,7 @@ class AddGroupsCompilerPass implements CompilerPassInterface
 {
     const SERVICE_ID_PREFIX = 'liip_monitor.check.';
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (!$container->hasParameter('liip_monitor.checks')) {
             return;
@@ -23,10 +23,7 @@ public function process(ContainerBuilder $container)
         $this->addGroupTags($container, $checkCollections, 'liip_monitor.check_collection');
     }
 
-    /**
-     * @return array
-     */
-    private function parseGroups(ContainerBuilder $container, array $data)
+    private function parseGroups(ContainerBuilder $container, array $data): array
     {
         $checks = [];
         $checkCollections = [];
@@ -56,7 +53,7 @@ private function parseGroups(ContainerBuilder $container, array $data)
      *
      * @param string $tag
      */
-    private function addGroupTags(ContainerBuilder $container, array $checks, $tag)
+    private function addGroupTags(ContainerBuilder $container, array $checks, $tag): void
     {
         foreach ($checks as $checkName => $groups) {
             $serviceId = self::SERVICE_ID_PREFIX.$checkName;
diff --git a/DependencyInjection/Compiler/AdditionalReporterCompilerPass.php b/DependencyInjection/Compiler/AdditionalReporterCompilerPass.php
index 335d46c4..15ea86f8 100644
--- a/DependencyInjection/Compiler/AdditionalReporterCompilerPass.php
+++ b/DependencyInjection/Compiler/AdditionalReporterCompilerPass.php
@@ -11,7 +11,7 @@
  */
 class AdditionalReporterCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (false === $container->hasParameter('liip_monitor.runners')) {
             return;
diff --git a/DependencyInjection/Compiler/CheckAssetsEnabledPass.php b/DependencyInjection/Compiler/CheckAssetsEnabledPass.php
index 27d0bf73..31c55a08 100644
--- a/DependencyInjection/Compiler/CheckAssetsEnabledPass.php
+++ b/DependencyInjection/Compiler/CheckAssetsEnabledPass.php
@@ -8,7 +8,7 @@
 
 class CheckAssetsEnabledPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if ($container->has('liip_monitor.health_controller') && !$container->has('assets.packages')) {
             throw new LogicException('Controller support cannot be enabled unless the frameworkbundle "assets" support is also enabled.');
diff --git a/DependencyInjection/Compiler/CheckCollectionTagCompilerPass.php b/DependencyInjection/Compiler/CheckCollectionTagCompilerPass.php
index 0ffb6c71..fd224588 100644
--- a/DependencyInjection/Compiler/CheckCollectionTagCompilerPass.php
+++ b/DependencyInjection/Compiler/CheckCollectionTagCompilerPass.php
@@ -8,7 +8,7 @@
 
 class CheckCollectionTagCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (false === $container->hasParameter('liip_monitor.default_group')) {
             return;
diff --git a/DependencyInjection/Compiler/CheckTagCompilerPass.php b/DependencyInjection/Compiler/CheckTagCompilerPass.php
index c36c2c99..413e6e58 100644
--- a/DependencyInjection/Compiler/CheckTagCompilerPass.php
+++ b/DependencyInjection/Compiler/CheckTagCompilerPass.php
@@ -8,7 +8,7 @@
 
 class CheckTagCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (false === $container->hasParameter('liip_monitor.default_group')) {
             return;
diff --git a/DependencyInjection/Compiler/GroupRunnersCompilerPass.php b/DependencyInjection/Compiler/GroupRunnersCompilerPass.php
index 1753450f..4b5e4ee4 100644
--- a/DependencyInjection/Compiler/GroupRunnersCompilerPass.php
+++ b/DependencyInjection/Compiler/GroupRunnersCompilerPass.php
@@ -7,7 +7,7 @@
 
 class GroupRunnersCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $noRunner = false === $container->hasDefinition('liip_monitor.runner');
         $noDefaultGroup = false === $container->hasParameter('liip_monitor.default_group');
@@ -45,10 +45,7 @@ public function process(ContainerBuilder $container)
         $container->setParameter('liip_monitor.runners', $runners);
     }
 
-    /**
-     * @return array
-     */
-    private function getGroups(array $services)
+    private function getGroups(array $services): array
     {
         $groups = [];
         foreach ($services as $serviceId => $tags) {
@@ -62,10 +59,7 @@ private function getGroups(array $services)
         return array_keys($groups);
     }
 
-    /**
-     * @return array
-     */
-    private function getGroupsFromParameter(ContainerBuilder $container)
+    private function getGroupsFromParameter(ContainerBuilder $container): array
     {
         $groups = [];
 
diff --git a/DependencyInjection/Compiler/MailerCompilerPass.php b/DependencyInjection/Compiler/MailerCompilerPass.php
index 67950571..335032e9 100644
--- a/DependencyInjection/Compiler/MailerCompilerPass.php
+++ b/DependencyInjection/Compiler/MailerCompilerPass.php
@@ -13,7 +13,7 @@
  */
 class MailerCompilerPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (false === $container->hasParameter('liip_monitor.mailer.enabled')) {
             return;
diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 0c63db6f..e11da28e 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -4,6 +4,7 @@
 
 use Doctrine\Bundle\MigrationsBundle\DoctrineMigrationsBundle;
 use Symfony\Component\Config\Definition\BaseNode;
+use Symfony\Component\Config\Definition\Builder\NodeDefinition;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 
@@ -19,10 +20,8 @@ class Configuration implements ConfigurationInterface
 {
     /**
      * Generates the configuration tree.
-     *
-     * @return TreeBuilder
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('liip_monitor');
 
@@ -86,7 +85,7 @@ public function getConfigTreeBuilder()
         return $treeBuilder;
     }
 
-    private function createGroupsNode()
+    private function createGroupsNode(): NodeDefinition
     {
         $builder = new TreeBuilder('groups');
 
@@ -440,7 +439,7 @@ private function createGroupsNode()
      * introduced at the same time. By checking if getDeprecation() exists,
      * we can determine the correct param count to use when calling setDeprecated.
      */
-    private static function getCustomErrorPagesControllerDeprecationMessage()
+    private static function getCustomErrorPagesControllerDeprecationMessage(): array
     {
         $message = 'The custom error page controller option is no longer used; the corresponding config parameter was deprecated in 2.13 and will be dropped in 3.0.';
 
diff --git a/DependencyInjection/DoctrineMigrations/DoctrineMigrationsLoader.php b/DependencyInjection/DoctrineMigrations/DoctrineMigrationsLoader.php
index f3172cc0..0028eafc 100644
--- a/DependencyInjection/DoctrineMigrations/DoctrineMigrationsLoader.php
+++ b/DependencyInjection/DoctrineMigrations/DoctrineMigrationsLoader.php
@@ -28,7 +28,7 @@ public function __construct()
             : new V3MigrationsLoader();
     }
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         if (!($this->loader instanceof CompilerPassInterface)) {
             return;
diff --git a/DependencyInjection/DoctrineMigrations/V2MigrationsLoader.php b/DependencyInjection/DoctrineMigrations/V2MigrationsLoader.php
index 91b0e3b0..1cfc8e0c 100644
--- a/DependencyInjection/DoctrineMigrations/V2MigrationsLoader.php
+++ b/DependencyInjection/DoctrineMigrations/V2MigrationsLoader.php
@@ -35,7 +35,7 @@ final class V2MigrationsLoader extends AbstractDoctrineMigrationsLoader implemen
      */
     private $migrationConfigurationsServices = [];
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         foreach ($this->migrationConfigurationsServices as $services) {
             [$configurationService, $configuration] = $services;
diff --git a/DependencyInjection/LiipMonitorExtension.php b/DependencyInjection/LiipMonitorExtension.php
index 3ed2a4be..68d52e09 100644
--- a/DependencyInjection/LiipMonitorExtension.php
+++ b/DependencyInjection/LiipMonitorExtension.php
@@ -30,7 +30,7 @@ public function __construct()
     /**
      * Loads the services based on your application configuration.
      */
-    public function load(array $configs, ContainerBuilder $container)
+    public function load(array $configs, ContainerBuilder $container): void
     {
         $loader = new Loader\XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('runner.xml');
@@ -96,7 +96,7 @@ public function load(array $configs, ContainerBuilder $container)
         $this->configureDoctrineMigrationsCheck($container, $containerParams);
     }
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $this->migrationsLoader->process($container);
     }
@@ -106,7 +106,7 @@ public function process(ContainerBuilder $container)
      * @param string $group
      * @param array  $values
      */
-    private function setParameters(ContainerBuilder $container, $checkName, $group, $values)
+    private function setParameters(ContainerBuilder $container, $checkName, $group, $values): void
     {
         $prefix = sprintf('%s.check.%s', $this->getAlias(), $checkName);
         switch ($checkName) {
@@ -161,10 +161,8 @@ private function setParameters(ContainerBuilder $container, $checkName, $group,
      *
      * @param ContainerBuilder $container The container
      * @param array            $params    Container params
-     *
-     * @return void
      */
-    private function configureDoctrineMigrationsCheck(ContainerBuilder $container, array $params)
+    private function configureDoctrineMigrationsCheck(ContainerBuilder $container, array $params): void
     {
         if (!$container->hasDefinition('liip_monitor.check.doctrine_migrations') || !isset($params['groups'])) {
             return;
@@ -186,7 +184,7 @@ private function configureDoctrineMigrationsCheck(ContainerBuilder $container, a
         }
     }
 
-    private function configureMailer(ContainerBuilder $container, array $config)
+    private function configureMailer(ContainerBuilder $container, array $config): void
     {
         if (false === $config['mailer']['enabled']) {
             return;
diff --git a/DoctrineMigrations/Configuration.php b/DoctrineMigrations/Configuration.php
index 16f4af1c..ed82953d 100644
--- a/DoctrineMigrations/Configuration.php
+++ b/DoctrineMigrations/Configuration.php
@@ -29,20 +29,16 @@ class Configuration extends BaseConfiguration
      * Set service container.
      *
      * @param ContainerInterface $container Service container
-     *
-     * @return void
      */
-    public function setContainer(ContainerInterface $container)
+    public function setContainer(ContainerInterface $container): void
     {
         $this->container = $container;
     }
 
     /**
      * Tune this configuration parameters according to migrations bundle.
-     *
-     * @return void
      */
-    public function configure()
+    public function configure(): void
     {
         if (null === self::$haveMigrationBundle) {
             self::$haveMigrationBundle = class_exists(DoctrineCommand::class);
diff --git a/Helper/AbstractMailReporter.php b/Helper/AbstractMailReporter.php
index c530f202..8cd2749f 100644
--- a/Helper/AbstractMailReporter.php
+++ b/Helper/AbstractMailReporter.php
@@ -41,22 +41,37 @@ public function __construct($recipients, $sender, $subject, $sendOnWarning = tru
         $this->sendOnWarning = $sendOnWarning;
     }
 
+    /**
+     * @return void
+     */
     public function onStart(ArrayObject $checks, $runnerConfig)
     {
     }
 
+    /**
+     * @return bool|void
+     */
     public function onBeforeRun(CheckInterface $check, $checkAlias = null)
     {
     }
 
+    /**
+     * @return bool|void
+     */
     public function onAfterRun(CheckInterface $check, ResultInterface $result, $checkAlias = null)
     {
     }
 
+    /**
+     * @return void
+     */
     public function onStop(ResultsCollection $results)
     {
     }
 
+    /**
+     * @return void
+     */
     public function onFinish(ResultsCollection $results)
     {
         if ($results->getUnknownCount() > 0) {
@@ -78,5 +93,5 @@ public function onFinish(ResultsCollection $results)
         }
     }
 
-    abstract protected function sendEmail(ResultsCollection $results);
+    abstract protected function sendEmail(ResultsCollection $results): void;
 }
diff --git a/Helper/ArrayReporter.php b/Helper/ArrayReporter.php
index edf1ab61..f9074c9b 100644
--- a/Helper/ArrayReporter.php
+++ b/Helper/ArrayReporter.php
@@ -21,22 +21,19 @@ class ArrayReporter implements ReporterInterface
     private $globalStatus = self::STATUS_OK;
     private $results = [];
 
-    /**
-     * @return array
-     */
-    public function getResults()
+    public function getResults(): array
     {
         return $this->results;
     }
 
-    /**
-     * @return string
-     */
-    public function getGlobalStatus()
+    public function getGlobalStatus(): string
     {
         return $this->globalStatus;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onAfterRun(CheckInterface $check, ResultInterface $result, $checkAlias = null)
     {
         switch (true) {
@@ -71,21 +68,33 @@ public function onAfterRun(CheckInterface $check, ResultInterface $result, $chec
         ];
     }
 
+    /**
+     * @return void
+     */
     public function onStart(\ArrayObject $checks, $runnerConfig)
     {
         return;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onBeforeRun(CheckInterface $check, $checkAlias = null)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onStop(ResultsCollection $results)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onFinish(ResultsCollection $results)
     {
         return;
diff --git a/Helper/ConsoleReporter.php b/Helper/ConsoleReporter.php
index 201eba2e..26f4d6c7 100644
--- a/Helper/ConsoleReporter.php
+++ b/Helper/ConsoleReporter.php
@@ -33,11 +33,14 @@ public function __construct(OutputInterface $output = null)
         $this->output = $output;
     }
 
-    public function setOutput(OutputInterface $output)
+    public function setOutput(OutputInterface $output): void
     {
         $this->output = $output;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onAfterRun(CheckInterface $check, ResultInterface $result, $checkAlias = null)
     {
         switch (true) {
@@ -66,21 +69,33 @@ public function onAfterRun(CheckInterface $check, ResultInterface $result, $chec
         $this->output->writeln('');
     }
 
+    /**
+     * @return void
+     */
     public function onStart(\ArrayObject $checks, $runnerConfig)
     {
         return;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onBeforeRun(CheckInterface $check, $checkAlias = null)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onStop(ResultsCollection $results)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onFinish(ResultsCollection $results)
     {
         return;
diff --git a/Helper/PathHelper.php b/Helper/PathHelper.php
index eee6d789..7ea4bb7c 100644
--- a/Helper/PathHelper.php
+++ b/Helper/PathHelper.php
@@ -13,10 +13,7 @@ public function __construct($assetsHelper, $routerHelper)
         $this->routerHelper = $routerHelper;
     }
 
-    /**
-     * @return array
-     */
-    public function generateRoutes(array $routes)
+    public function generateRoutes(array $routes): array
     {
         $ret = [];
 
@@ -36,10 +33,7 @@ public function generateRoutes(array $routes)
         return $ret;
     }
 
-    /**
-     * @return string
-     */
-    public function getRoutesJs(array $routes)
+    public function getRoutesJs(array $routes): string
     {
         $script = '<script type="text/javascript" charset="utf-8">';
         $script .= "var api = {};\n";
@@ -51,10 +45,8 @@ public function getRoutesJs(array $routes)
 
     /**
      * @param string[] $paths
-     *
-     * @return string
      */
-    public function getScriptTags(array $paths)
+    public function getScriptTags(array $paths): string
     {
         $ret = '';
         foreach ($paths as $path) {
@@ -66,10 +58,8 @@ public function getScriptTags(array $paths)
 
     /**
      * @param string[] $paths
-     *
-     * @return string
      */
-    public function getStyleTags(array $paths)
+    public function getStyleTags(array $paths): string
     {
         $ret = '';
         foreach ($paths as $path) {
diff --git a/Helper/RawConsoleReporter.php b/Helper/RawConsoleReporter.php
index 84ae26ed..c59ed44c 100644
--- a/Helper/RawConsoleReporter.php
+++ b/Helper/RawConsoleReporter.php
@@ -33,11 +33,14 @@ public function __construct(OutputInterface $output = null)
         $this->output = $output;
     }
 
-    public function setOutput(OutputInterface $output)
+    public function setOutput(OutputInterface $output): void
     {
         $this->output = $output;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onAfterRun(CheckInterface $check, ResultInterface $result, $checkAlias = null)
     {
         switch (true) {
@@ -62,29 +65,38 @@ public function onAfterRun(CheckInterface $check, ResultInterface $result, $chec
         $this->output->writeln(sprintf(' %s', $check->getLabel().$performanceData));
     }
 
-    /**
-     * @return string
-     */
-    protected function getNagiosPerformanceData()
+    protected function getNagiosPerformanceData(): string
     {
         return '';
     }
 
+    /**
+     * @return void
+     */
     public function onStart(\ArrayObject $checks, $runnerConfig)
     {
         return;
     }
 
+    /**
+     * @return bool|void
+     */
     public function onBeforeRun(CheckInterface $check, $checkAlias = null)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onStop(ResultsCollection $results)
     {
         return;
     }
 
+    /**
+     * @return void
+     */
     public function onFinish(ResultsCollection $results)
     {
         return;
diff --git a/Helper/RunnerManager.php b/Helper/RunnerManager.php
index 063b0e87..6bbafc11 100644
--- a/Helper/RunnerManager.php
+++ b/Helper/RunnerManager.php
@@ -17,10 +17,8 @@ public function __construct(ContainerInterface $container)
 
     /**
      * @param string|null $group
-     *
-     * @return Runner|null
      */
-    public function getRunner($group)
+    public function getRunner($group): ?Runner
     {
         $runnerServiceId = $this->getRunnerServiceId($group);
 
@@ -30,7 +28,7 @@ public function getRunner($group)
     /**
      * @return array|Runner[] key/value $group/$runner
      */
-    public function getRunners()
+    public function getRunners(): array
     {
         $runnerServiceIds = $this->container->getParameter('liip_monitor.runners');
 
@@ -48,7 +46,7 @@ public function getRunners()
     /**
      * @return array|string[]
      */
-    public function getGroups()
+    public function getGroups(): array
     {
         $runnerServiceIds = $this->container->getParameter('liip_monitor.runners');
 
@@ -63,20 +61,15 @@ public function getGroups()
         return $groups;
     }
 
-    /**
-     * @return string
-     */
-    public function getDefaultGroup()
+    public function getDefaultGroup(): string
     {
         return $this->container->getParameter('liip_monitor.default_group');
     }
 
     /**
      * @param string|null $group
-     *
-     * @return string|null
      */
-    private function getRunnerServiceId($group)
+    private function getRunnerServiceId($group): ?string
     {
         if (null === $group) {
             $group = $this->getDefaultGroup();
@@ -87,10 +80,7 @@ private function getRunnerServiceId($group)
         return $this->container->has($runnerServiceId) ? $runnerServiceId : null;
     }
 
-    /**
-     * @return array
-     */
-    public function getReporters()
+    public function getReporters(): array
     {
         $runners = $this->getRunners();
         $reporters = [];
diff --git a/Helper/SwiftMailerReporter.php b/Helper/SwiftMailerReporter.php
index d7995581..4418c721 100644
--- a/Helper/SwiftMailerReporter.php
+++ b/Helper/SwiftMailerReporter.php
@@ -28,7 +28,7 @@ public function __construct(Swift_Mailer $mailer, $recipients, $sender, $subject
         parent::__construct($recipients, $sender, $subject, $sendOnWarning);
     }
 
-    protected function sendEmail(ResultsCollection $results)
+    protected function sendEmail(ResultsCollection $results): void
     {
         $body = '';
 
diff --git a/LiipMonitorBundle.php b/LiipMonitorBundle.php
index a59e3b0d..504e9c1b 100644
--- a/LiipMonitorBundle.php
+++ b/LiipMonitorBundle.php
@@ -15,7 +15,7 @@
 
 class LiipMonitorBundle extends Bundle
 {
-    public function build(ContainerBuilder $container)
+    public function build(ContainerBuilder $container): void
     {
         if (method_exists($container, 'registerForAutoconfiguration')) {
             $container->registerForAutoconfiguration(CheckInterface::class)
diff --git a/Runner.php b/Runner.php
index 60a5d144..991bb5fc 100644
--- a/Runner.php
+++ b/Runner.php
@@ -15,12 +15,12 @@ class Runner extends BaseRunner
     /**
      * @param string $alias
      */
-    public function addAdditionalReporter($alias, ReporterInterface $reporter)
+    public function addAdditionalReporter($alias, ReporterInterface $reporter): void
     {
         $this->additionalReporters[$alias] = $reporter;
     }
 
-    public function useAdditionalReporters(array $aliases)
+    public function useAdditionalReporters(array $aliases): void
     {
         foreach ($this->additionalReporters as $alias => $reporter) {
             if (in_array($alias, $aliases)) {
@@ -29,10 +29,7 @@ public function useAdditionalReporters(array $aliases)
         }
     }
 
-    /**
-     * @return array
-     */
-    public function getAdditionalReporters()
+    public function getAdditionalReporters(): array
     {
         return $this->additionalReporters;
     }
diff --git a/Tests/Check/ExpressionTest.php b/Tests/Check/ExpressionTest.php
index 6800033e..8a23f564 100644
--- a/Tests/Check/ExpressionTest.php
+++ b/Tests/Check/ExpressionTest.php
@@ -16,7 +16,7 @@ class ExpressionTest extends \PHPUnit\Framework\TestCase
     /**
      * @dataProvider checkResultProvider
      */
-    public function testCheckResult($warningCheck, $criticalCheck, $warningMessage, $criticalMessage, $expectedResultClass, $expectedMessage)
+    public function testCheckResult($warningCheck, $criticalCheck, $warningMessage, $criticalMessage, $expectedResultClass, $expectedMessage): void
     {
         $check = new Expression('foo', $warningCheck, $criticalCheck, $warningMessage, $criticalMessage);
         $this->assertSame('foo', $check->getLabel());
@@ -27,7 +27,7 @@ public function testCheckResult($warningCheck, $criticalCheck, $warningMessage,
         $this->assertSame($expectedMessage, $result->getMessage());
     }
 
-    public function checkResultProvider()
+    public function checkResultProvider(): array
     {
         return [
             ['true', 'true', null, null, Success::class, ''],
diff --git a/Tests/Check/RedisCollectionTest.php b/Tests/Check/RedisCollectionTest.php
index 07189b6f..4c1a6ee0 100644
--- a/Tests/Check/RedisCollectionTest.php
+++ b/Tests/Check/RedisCollectionTest.php
@@ -16,7 +16,7 @@ final class RedisCollectionTest extends TestCase
      * @test
      * @dataProvider provideDsnWithAut
      */
-    public function handleDsnWithAuth(string $dsn)
+    public function handleDsnWithAuth(string $dsn): void
     {
         $config = [
           'dsn' => $dsn,
@@ -34,7 +34,7 @@ public function handleDsnWithAuth(string $dsn)
         $this->assertAuthPropertyValue($check, self::AUTH);
     }
 
-    private function assertAuthPropertyValue(Redis $check, string $auth)
+    private function assertAuthPropertyValue(Redis $check, string $auth): void
     {
         try {
             $refClass = new ReflectionClass($check);
diff --git a/Tests/DependencyInjection/Compiler/AddGroupsCompilerPassTest.php b/Tests/DependencyInjection/Compiler/AddGroupsCompilerPassTest.php
index b148599d..c5392b3e 100644
--- a/Tests/DependencyInjection/Compiler/AddGroupsCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/AddGroupsCompilerPassTest.php
@@ -9,7 +9,7 @@
 
 class AddGroupsCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testProcess()
+    public function testProcess(): void
     {
         $checkConfig = [
             'groups' => [
diff --git a/Tests/DependencyInjection/Compiler/AdditionalReporterCompilerPassTest.php b/Tests/DependencyInjection/Compiler/AdditionalReporterCompilerPassTest.php
index 26419f59..6a1ffc83 100644
--- a/Tests/DependencyInjection/Compiler/AdditionalReporterCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/AdditionalReporterCompilerPassTest.php
@@ -13,7 +13,7 @@
  */
 class AdditionalReporterCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testProcessWithAlias()
+    public function testProcessWithAlias(): void
     {
         $runner = new Definition();
         $this->setDefinition('liip_monitor.runner_default', $runner);
@@ -35,7 +35,7 @@ public function testProcessWithAlias()
         );
     }
 
-    public function testProcessWithoutAlias()
+    public function testProcessWithoutAlias(): void
     {
         $runner = new Definition();
         $this->setDefinition('liip_monitor.runner_default', $runner);
diff --git a/Tests/DependencyInjection/Compiler/CheckCollectionTagCompilerPassTest.php b/Tests/DependencyInjection/Compiler/CheckCollectionTagCompilerPassTest.php
index 37ac9cf5..c1a0b563 100644
--- a/Tests/DependencyInjection/Compiler/CheckCollectionTagCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/CheckCollectionTagCompilerPassTest.php
@@ -14,7 +14,7 @@
  */
 class CheckCollectionTagCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testProcess()
+    public function testProcess(): void
     {
         $defaultGroup = 'grupo_predeterminado';
 
diff --git a/Tests/DependencyInjection/Compiler/CheckTagCompilerPassTest.php b/Tests/DependencyInjection/Compiler/CheckTagCompilerPassTest.php
index a09610bc..eddf277e 100644
--- a/Tests/DependencyInjection/Compiler/CheckTagCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/CheckTagCompilerPassTest.php
@@ -14,7 +14,7 @@
  */
 class CheckTagCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testProcess()
+    public function testProcess(): void
     {
         $defaultGroup = 'gruppo_predefinito';
 
diff --git a/Tests/DependencyInjection/Compiler/GroupRunnersCompilerPassTest.php b/Tests/DependencyInjection/Compiler/GroupRunnersCompilerPassTest.php
index 1d32226a..9524b00a 100644
--- a/Tests/DependencyInjection/Compiler/GroupRunnersCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/GroupRunnersCompilerPassTest.php
@@ -9,7 +9,7 @@
 
 class GroupRunnersCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testProcess()
+    public function testProcess(): void
     {
         $defaultGroup = 'groupe_par_défaut';
 
diff --git a/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php b/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
index 9a85c234..e2f09596 100644
--- a/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
@@ -13,7 +13,7 @@
 
 class MailerCompilerPassTest extends AbstractCompilerPassTestCase
 {
-    public function testDisabledMailer()
+    public function testDisabledMailer(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', false);
 
@@ -23,7 +23,7 @@ public function testDisabledMailer()
         $this->assertContainerBuilderNotHasService('liip_monitor.reporter.swift_mailer');
     }
 
-    public function testSwiftMailer()
+    public function testSwiftMailer(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->setDefinition('mailer', new Definition(\Swift_Mailer::class));
@@ -65,7 +65,7 @@ public function testSwiftMailer()
         );
     }
 
-    public function testSwiftMailerWithAliasDefinition()
+    public function testSwiftMailerWithAliasDefinition(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->setDefinition('swift.mailer', new Definition(\Swift_Mailer::class));
@@ -78,7 +78,7 @@ public function testSwiftMailerWithAliasDefinition()
         $this->assertContainerBuilderHasService('liip_monitor.reporter.swift_mailer', SwiftMailerReporter::class);
     }
 
-    public function testSymfonyMailer()
+    public function testSymfonyMailer(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->setDefinition('mailer', new Definition(MailerInterface::class));
@@ -120,7 +120,7 @@ public function testSymfonyMailer()
         );
     }
 
-    public function testSymfonyMailerWithAliasDefinition()
+    public function testSymfonyMailerWithAliasDefinition(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->setDefinition('symfony.mailer', new Definition(MailerInterface::class));
@@ -133,7 +133,7 @@ public function testSymfonyMailerWithAliasDefinition()
         $this->assertContainerBuilderHasService('liip_monitor.reporter.symfony_mailer', SymfonyMailerReporter::class);
     }
 
-    public function testMailerWithoutPackage()
+    public function testMailerWithoutPackage(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->expectExceptionMessage('To enable mail reporting you have to install the "swiftmailer/swiftmailer" or "symfony/mailer".');
@@ -143,7 +143,7 @@ public function testMailerWithoutPackage()
         $this->compile();
     }
 
-    public function testMailerMissingAliasDefinition()
+    public function testMailerMissingAliasDefinition(): void
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
         $this->setDefinition('swift.mailer', new Definition(\Swift_Mailer::class));
diff --git a/Tests/DependencyInjection/LiipMonitorExtensionTest.php b/Tests/DependencyInjection/LiipMonitorExtensionTest.php
index 11e7b085..f8a2e095 100644
--- a/Tests/DependencyInjection/LiipMonitorExtensionTest.php
+++ b/Tests/DependencyInjection/LiipMonitorExtensionTest.php
@@ -58,7 +58,7 @@ protected function setUp(): void
     /**
      * @dataProvider checkProvider
      */
-    public function testChecksLoaded($name, $config, $checkClass, $checkAlias = null, $checkCount = 1)
+    public function testChecksLoaded($name, $config, $checkClass, $checkAlias = null, $checkCount = 1): void
     {
         // skip checks for missing classes
         if (!class_exists($checkClass)) {
@@ -79,7 +79,7 @@ public function testChecksLoaded($name, $config, $checkClass, $checkAlias = null
         $this->assertInstanceOf($checkClass, $runner->getCheck($checkAlias));
     }
 
-    public function testDefaultNoChecks()
+    public function testDefaultNoChecks(): void
     {
         $this->load();
         $this->compile();
@@ -87,7 +87,7 @@ public function testDefaultNoChecks()
         $this->assertCount(0, $this->container->get('liip_monitor.runner')->getChecks());
     }
 
-    public function testDefaultGroupParameterHasNoChecks()
+    public function testDefaultGroupParameterHasNoChecks(): void
     {
         $this->load();
         $this->compile();
@@ -96,7 +96,7 @@ public function testDefaultGroupParameterHasNoChecks()
         $this->assertSame('default', $this->container->getParameter('liip_monitor.default_group'));
     }
 
-    public function testDefaultGroupParameter()
+    public function testDefaultGroupParameter(): void
     {
         $this->load(['checks' => ['php_extensions' => ['foo']]]);
         $this->compile();
@@ -105,7 +105,7 @@ public function testDefaultGroupParameter()
         $this->assertSame('default', $this->container->getParameter('liip_monitor.default_group'));
     }
 
-    public function testDefaultGroupParameterCustom()
+    public function testDefaultGroupParameterCustom(): void
     {
         $this->load(['checks' => ['php_extensions' => ['foo']], 'default_group' => 'foo_bar']);
         $this->compile();
@@ -114,7 +114,7 @@ public function testDefaultGroupParameterCustom()
         $this->assertSame('foo_bar', $this->container->getParameter('liip_monitor.default_group'));
     }
 
-    public function testEnableController()
+    public function testEnableController(): void
     {
         $this->load();
 
@@ -125,7 +125,7 @@ public function testEnableController()
         $this->assertTrue($this->container->has('liip_monitor.health_controller'));
     }
 
-    public function testDisabledDefaultMailer()
+    public function testDisabledDefaultMailer(): void
     {
         $this->load();
 
@@ -136,7 +136,7 @@ public function testDisabledDefaultMailer()
         $this->assertFalse($this->container->hasParameter('liip_monitor.mailer.send_on_warning'));
     }
 
-    public function testDisabledMailer()
+    public function testDisabledMailer(): void
     {
         $this->load(
             [
@@ -157,7 +157,7 @@ public function testDisabledMailer()
         $this->assertFalse($this->container->hasParameter('liip_monitor.mailer.send_on_warning'));
     }
 
-    public function testEnabledMailer()
+    public function testEnabledMailer(): void
     {
         $this->load(
             [
@@ -181,14 +181,14 @@ public function testEnabledMailer()
     /**
      * @dataProvider mailerConfigProvider
      */
-    public function testInvalidMailerConfig($config)
+    public function testInvalidMailerConfig($config): void
     {
         $this->expectException(InvalidConfigurationException::class);
 
         $this->load($config);
     }
 
-    public function mailerConfigProvider()
+    public function mailerConfigProvider(): array
     {
         return [
             [
@@ -213,7 +213,7 @@ public function mailerConfigProvider()
     /**
      * @dataProvider invalidCheckProvider
      */
-    public function testInvalidExpressionConfig(array $config)
+    public function testInvalidExpressionConfig(array $config): void
     {
         $this->expectException(InvalidConfigurationException::class);
 
@@ -221,7 +221,7 @@ public function testInvalidExpressionConfig(array $config)
         $this->compile();
     }
 
-    public function invalidCheckProvider()
+    public function invalidCheckProvider(): array
     {
         return [
             [['foo']],
@@ -230,7 +230,7 @@ public function invalidCheckProvider()
         ];
     }
 
-    public function checkProvider()
+    public function checkProvider(): array
     {
         return [
             ['php_extensions', ['foo'], ExtensionLoaded::class],
diff --git a/Tests/Helper/PathHelperTest.php b/Tests/Helper/PathHelperTest.php
index f0a2fa4e..b1e375ad 100644
--- a/Tests/Helper/PathHelperTest.php
+++ b/Tests/Helper/PathHelperTest.php
@@ -7,14 +7,14 @@
 
 class PathHelperTest extends WebTestCase
 {
-    public static function getKernelClass()
+    public static function getKernelClass(): string
     {
         require_once __DIR__.'/../app/AppKernel.php';
 
         return 'AppKernel';
     }
 
-    public function testGenerateRoutes()
+    public function testGenerateRoutes(): void
     {
         $environment = 'symfony'.Kernel::MAJOR_VERSION;
         $client = static::createClient(['environment' => $environment]);
diff --git a/Tests/Helper/RunnerManagerTest.php b/Tests/Helper/RunnerManagerTest.php
index bd8a469a..65637461 100644
--- a/Tests/Helper/RunnerManagerTest.php
+++ b/Tests/Helper/RunnerManagerTest.php
@@ -16,7 +16,7 @@ class RunnerManagerTest extends \PHPUnit\Framework\TestCase
      */
     private $runnerManager;
 
-    public function groupProvider()
+    public function groupProvider(): array
     {
         return [
             [null],
@@ -30,7 +30,7 @@ public function groupProvider()
      *
      * @param string $group
      */
-    public function testGetRunner($group)
+    public function testGetRunner($group): void
     {
         $this->container
             ->expects($this->any())
@@ -57,7 +57,7 @@ public function testGetRunner($group)
         $this->assertSame($expectedResult, $result);
     }
 
-    public function testGetRunnerReturnsNull()
+    public function testGetRunnerReturnsNull(): void
     {
         $this->container
             ->expects($this->any())
@@ -70,7 +70,7 @@ public function testGetRunnerReturnsNull()
         $this->assertNull($result);
     }
 
-    public function testGetRunners()
+    public function testGetRunners(): void
     {
         $this->container
             ->expects($this->any())
@@ -100,7 +100,7 @@ public function testGetRunners()
         $this->assertSame($runner2, $result['group_2']);
     }
 
-    public function testGetGroups()
+    public function testGetGroups(): void
     {
         $this->container
             ->expects($this->any())
@@ -116,7 +116,7 @@ public function testGetGroups()
         $this->assertContains('group_2', $result);
     }
 
-    public function testGetDefaultGroup()
+    public function testGetDefaultGroup(): void
     {
         $expectedResult = 'default';
 
diff --git a/Tests/Helper/SwiftMailerReporterTest.php b/Tests/Helper/SwiftMailerReporterTest.php
index e898760b..d229d099 100644
--- a/Tests/Helper/SwiftMailerReporterTest.php
+++ b/Tests/Helper/SwiftMailerReporterTest.php
@@ -21,7 +21,7 @@ class SwiftMailerReporterTest extends \PHPUnit\Framework\TestCase
     /**
      * @dataProvider sendNoEmailProvider
      */
-    public function testSendNoEmail(ResultInterface $result, $sendOnWarning)
+    public function testSendNoEmail(ResultInterface $result, $sendOnWarning): void
     {
         $mailer = $this->prophesize('Swift_Mailer');
         $mailer->send()->shouldNotBeCalled();
@@ -36,7 +36,7 @@ public function testSendNoEmail(ResultInterface $result, $sendOnWarning)
     /**
      * @dataProvider sendEmailProvider
      */
-    public function testSendEmail(ResultInterface $result, $sendOnWarning)
+    public function testSendEmail(ResultInterface $result, $sendOnWarning): void
     {
         $mailer = $this->prophesize('Swift_Mailer');
         $mailer->send(Argument::type('Swift_Message'))->shouldBeCalled();
@@ -48,7 +48,7 @@ public function testSendEmail(ResultInterface $result, $sendOnWarning)
         $reporter->onFinish($results);
     }
 
-    public function sendEmailProvider()
+    public function sendEmailProvider(): array
     {
         return [
             [new Failure(), true],
@@ -58,7 +58,7 @@ public function sendEmailProvider()
         ];
     }
 
-    public function sendNoEmailProvider()
+    public function sendNoEmailProvider(): array
     {
         return [
             [new Success(), true],
diff --git a/Tests/Helper/SymfonyMailerReporterTest.php b/Tests/Helper/SymfonyMailerReporterTest.php
index a08a07fb..cbc39e3a 100644
--- a/Tests/Helper/SymfonyMailerReporterTest.php
+++ b/Tests/Helper/SymfonyMailerReporterTest.php
@@ -31,7 +31,7 @@ protected function setUp(): void
     /**
      * @dataProvider getTestData
      */
-    public function testSendMail(array $recipients, string $sender, string $subject)
+    public function testSendMail(array $recipients, string $sender, string $subject): void
     {
         $reporter = new SymfonyMailerReporter($this->mailer->reveal(), $recipients, $sender, $subject);
 
diff --git a/Tests/LiipMonitorBundleTest.php b/Tests/LiipMonitorBundleTest.php
index 5e8c7b7d..08c9b09a 100644
--- a/Tests/LiipMonitorBundleTest.php
+++ b/Tests/LiipMonitorBundleTest.php
@@ -23,7 +23,7 @@ class LiipMonitorBundleTest extends \PHPUnit\Framework\TestCase
     /**
      * Test bundle build to add all required compiler passes.
      */
-    public function testBuildWithCompilerPasses()
+    public function testBuildWithCompilerPasses(): void
     {
         $compilerPasses = [
             'Liip\MonitorBundle\DependencyInjection\Compiler\CheckAssetsEnabledPass' => true,
diff --git a/Tests/RunnerTest.php b/Tests/RunnerTest.php
index b53a0489..a51100ea 100644
--- a/Tests/RunnerTest.php
+++ b/Tests/RunnerTest.php
@@ -10,7 +10,7 @@
  */
 class RunnerTest extends \PHPUnit\Framework\TestCase
 {
-    public function testAdditionalReporters()
+    public function testAdditionalReporters(): void
     {
         $runner = new Runner();
 
diff --git a/Tests/app/AppKernel.php b/Tests/app/AppKernel.php
index a29b1022..99ff3fe7 100644
--- a/Tests/app/AppKernel.php
+++ b/Tests/app/AppKernel.php
@@ -8,10 +8,7 @@
  */
 class AppKernel extends Kernel
 {
-    /**
-     * @return array
-     */
-    public function registerBundles()
+    public function registerBundles(): array
     {
         return [
             new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
@@ -20,12 +17,12 @@ public function registerBundles()
         ];
     }
 
-    public function registerContainerConfiguration(LoaderInterface $loader)
+    public function registerContainerConfiguration(LoaderInterface $loader): void
     {
         $loader->load(__DIR__.'/config_'.$this->environment.'.yml');
     }
 
-    public function getProjectDir()
+    public function getProjectDir(): string
     {
         return __DIR__;
     }