diff --git a/.wp-env.json b/.wp-env.json
index 1f957a7..1c12dd9 100644
--- a/.wp-env.json
+++ b/.wp-env.json
@@ -1,9 +1,10 @@
 {
-  "core": null,
-  "phpVersion": "8.0",
+  "core": "WordPress/WordPress",
+  "phpVersion": "8.1",
   "plugins": [ "." ],
   "env": {
     "tests": {
+      "phpVersion": "8.1",
       "config": {
         "FS_METHOD": "direct",
         "WP_DEBUG": true,
diff --git a/custom-post-types-taxonomies.php b/custom-post-types-taxonomies.php
index ba7c929..c512737 100644
--- a/custom-post-types-taxonomies.php
+++ b/custom-post-types-taxonomies.php
@@ -23,6 +23,7 @@
 
 declare( strict_types=1 );
 
+use Custom_PTT\Container_Singleton;
 use Custom_PTT\Plugin_Factory;
 
 if ( ! defined( 'ABSPATH' ) ) {
@@ -65,11 +66,7 @@
  * @throws Exception
  */
 function bootstrap_plugin(): void {
-
-	$container_builder = new DI\ContainerBuilder();
-	$container_builder->addDefinitions( __DIR__ . '/config/di-config.php' );
-	$container = $container_builder->build();
-
+	$container = Container_Singleton::get_instance();
 	Plugin_Factory::create( $container )
 		->boot();
 }
diff --git a/includes/Container_Singleton.php b/includes/Container_Singleton.php
new file mode 100644
index 0000000..30f6a96
--- /dev/null
+++ b/includes/Container_Singleton.php
@@ -0,0 +1,52 @@
+<?php
+
+declare( strict_types=1 );
+
+namespace Custom_PTT;
+
+use DI\Container;
+use DI\ContainerBuilder;
+use Exception;
+
+/**
+ * Container_Singleton class.
+ *
+ * This class is a placeholder for a singleton container instance.
+ *
+ * @package Custom_PTT
+ * @since 0.2.1
+ */
+class Container_Singleton {
+	/**
+	 * The Container instance.
+	 *
+	 * @var Container|null
+	 *
+	 * @since 0.2.1
+	 */
+	private static ?Container $container = null;
+
+	/**
+	 * Prevent class from being instantiated.
+	 * @since 0.2.1
+	 */
+	private function __construct() {}
+
+	/**
+	 * Get the Container instance.
+	 *
+	 * @return Container
+	 * @throws Exception
+	 *
+	 * @since 0.2.1
+	 */
+	public static function get_instance(): Container {
+		if ( null === static::$container ) {
+			$container_builder = new ContainerBuilder();
+			$container_builder->addDefinitions( __DIR__ . '/../config/di-config.php' );
+			static::$container = $container_builder->build();
+		}
+
+		return static::$container;
+	}
+}
diff --git a/tests/unit/Container_Singleton_Test.php b/tests/unit/Container_Singleton_Test.php
new file mode 100644
index 0000000..219fbd0
--- /dev/null
+++ b/tests/unit/Container_Singleton_Test.php
@@ -0,0 +1,71 @@
+<?php
+
+declare( strict_types=1 );
+
+namespace Custom_PTT\Tests\Unit;
+
+use Custom_PTT\Container_Singleton;
+use DI\Container;
+use Exception;
+use ReflectionClass;
+use WP_UnitTestCase;
+
+/**
+ * Class Container_Singleton_Test
+ *
+ * @package Custom_PTT\Tests\Unit
+ * @since 0.2.1
+ */
+class Container_Singleton_Test extends WP_UnitTestCase {
+
+	/**
+	 * Resets the container instance before each test, as it's created on plugin bootstrap
+	 *
+	 * @return void
+	 *
+	 * @since 0.2.1
+	 */
+	public function setUp(): void {
+		parent::setUp();
+
+		$reflection = new ReflectionClass( Container_Singleton::class );
+		$container  = $reflection->getProperty( 'container' );
+		$container->setAccessible( true );
+		$container->setValue( null, null );
+	}
+
+	/**
+	 * Test that get_instance returns a Container instance.
+	 *
+	 * @throws Exception
+	 *
+	 * @since 0.2.1
+	 */
+	public function test_get_instance_returns_container_instance() {
+		$instance = Container_Singleton::get_instance();
+		$this->assertInstanceOf( Container::class, $instance );
+	}
+
+	/**
+	 * Test that get_instance always returns the same instance.
+	 *
+	 * @throws Exception
+	 *
+	 * @since 0.2.1
+	 */
+	public function test_get_instance_returns_same_instance() {
+		$first_call_instance  = Container_Singleton::get_instance();
+		$second_call_instance = Container_Singleton::get_instance();
+
+		$this->assertSame( $first_call_instance, $second_call_instance );
+	}
+
+	/**
+	 * @return void
+	 *
+	 * @since 0.2.1
+	 */
+	public function tearDown(): void {
+		parent::tearDown();
+	}
+}
diff --git a/tests/unit/Plugin_Test.php b/tests/unit/Plugin_Test.php
index dc223f5..56533cd 100644
--- a/tests/unit/Plugin_Test.php
+++ b/tests/unit/Plugin_Test.php
@@ -4,22 +4,108 @@
 
 namespace Custom_PTT\Tests\Unit;
 
+use Custom_PTT\Container_Singleton;
 use Custom_PTT\Plugin;
+use Custom_PTT\Plugin_Factory;
 use DI\Container;
+use DI\DependencyException;
+use DI\NotFoundException;
+use Exception;
 use WP_UnitTestCase;
 
+/**
+ * Class Plugin_Test
+ *
+ * @package Custom_PTT\Tests\Unit
+ * @since 0.1.0-alpha
+ */
 class Plugin_Test extends WP_UnitTestCase {
 
-	private Plugin $plugin;
+	/**
+	 * Container instance.
+	 *
+	 * @var Container
+	 *
+	 * @since 0.2.1
+	 */
 	private Container $container;
 
+	/**
+	 * Plugin instance.
+	 *
+	 * @var Plugin
+	 *
+	 * @since 0.2.1
+	 */
+	private Plugin $plugin;
+
+	/**
+	 * Set up
+	 *
+	 * @return void
+	 *
+	 * @throws Exception
+	 * @since 0.1.0-alpha
+	 */
 	public function setUp(): void {
 		parent::setUp();
 
-		$this->container = $this->createMock( Container::class );
-		$this->plugin    = new Plugin( $this->container );
+		$this->container = Container_Singleton::get_instance();
+		$this->plugin    = Plugin_Factory::create( $this->container );
+	}
+
+	/**
+	 * Test plugin instance is created
+	 *
+	 * @return void
+	 *
+	 * @since 0.2.1
+	 */
+	public function test_plugin_instance_is_created() {
+		$this->assertInstanceOf( Plugin::class, $this->plugin );
+	}
+
+	/**
+	 * Test boot register activation and deactivation hooks
+	 *
+	 * @throws Exception
+	 *
+	 * @since 0.2.1
+	 */
+	public function test_boot_method_registers_hooks() {
+
+		$this->plugin->boot();
+
+		$file = plugin_basename( CUSTOM_PTT_FILE );
+
+		$this->assertEquals( 10, has_action( 'activate_' . $file, array( $this->plugin, 'on_activation' ) ) );
+		$this->assertEquals( 10, has_action( 'deactivate_' . $file, array( $this->plugin, 'on_deactivation' ) ) );
+	}
+
+	/**
+	 * Test all services are registered
+	 *
+	 * @since 0.2.1
+	 */
+	public function test_register_services_method_registers_services() {
+		$services = $this->container->getKnownEntryNames();
+
+		if ( empty( $services ) ) {
+			$this->fail( 'No services found' );
+		}
+
+		foreach ( $services as $service ) {
+			$this->assertTrue( $this->container->has( $service ) );
+		}
 	}
 
+	/**
+	 * Tear down
+	 *
+	 * @return void
+	 *
+	 * @since 0.1.0-alpha
+	 */
 	public function tearDown(): void {
 		parent::tearDown();
 	}
diff --git a/tests/unit/bootstrap.php b/tests/unit/bootstrap.php
index 425f2c9..37ef392 100644
--- a/tests/unit/bootstrap.php
+++ b/tests/unit/bootstrap.php
@@ -1,21 +1,34 @@
 <?php
 
+
+define( 'TESTS_PLUGIN_DIR', dirname( __DIR__, 2 ) );
+$_test_root = getenv( 'WP_TESTS_DIR' );
+
 if ( false === getenv( 'WP_TESTS_DIR' ) ) {
 	exit( 'WP_TESTS_DIR environment variable is not set. Please set it to the root of your WordPress installation.' );
 }
 
-define( 'TESTS_PLUGIN_DIR', dirname( __DIR__, 2 ) );
-
 if ( ! file_exists( TESTS_PLUGIN_DIR . '/vendor/autoload.php' ) ) {
 	exit( 'The vendor directory is missing. Please run composer install.' );
 }
 
+if ( ! file_exists( $_test_root . '/includes/bootstrap.php' ) ) {
+	exit( 'Could not load /includes/bootstrap.php' );
+}
+
 require TESTS_PLUGIN_DIR . '/vendor/autoload.php';
 
-$_test_root = getenv( 'WP_TESTS_DIR' );
+define( 'WP_TESTS_PHPUNIT_POLYFILLS_PATH', dirname( __DIR__, 2 ) . '/vendor/yoast/phpunit-polyfills' );
 
-if ( ! file_exists( $_test_root . '/includes/bootstrap.php' ) ) {
-	exit( 'Could not load /includes/bootstrap.php' );
+require_once $_test_root . '/includes/functions.php';
+
+/**
+ * Manually load the plugin being tested.
+ */
+function _manually_load_plugin(): void {
+	require dirname( __DIR__, 2 ) . '/custom-post-types-taxonomies.php';
 }
 
+tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );
+
 require $_test_root . '/includes/bootstrap.php';