And account for bad experiment names too

src/SeatGeek/Sixpack/Session/Base.php

@@ -3,6 +3,7 @@
 namespace SeatGeek\Sixpack\Session;
 
 use SeatGeek\Sixpack\Response;
+use SeatGeek\Sixpack\Session\Exception\InvalidExperimentNameException;
 use SeatGeek\Sixpack\Session\Exception\InvalidForcedAlternativeException;
 use \InvalidArgumentException;
 
@@ -209,7 +210,7 @@ protected function getIpAddress()
     protected function sendRequest($endpoint, $params = array())
     {
         if (isset($params["experiment"]) && !preg_match('#^[a-z0-9][a-z0-9\-_ ]*$#i', $params["experiment"])) {
-            throw new \Exception("Invalid Experiment Name: " . $params["experiment"]);
+            throw new InvalidExperimentNameException($params["experiment"]);
         }
 
         $params = array_merge(array(

src/SeatGeek/Sixpack/Session/Exception/InvalidExperimentNameException.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace SeatGeek\Sixpack\Session\Exception;
+
+use \Exception;
+
+/**
+ * Used when an experiement name is deemed invalid
+ */
+class InvalidExperimentNameException extends Exception
+{
+    /**
+     * The sprintf pattern for when an exception is thrown
+     *
+     * @var string
+     */
+    protected $messageTemplate = "The experiement name \"%s\" is invalid";
+
+    /**
+     * Constructor
+     *
+     * @param string|array If passed, it's the experiment name
+     * @param int $code The exception code
+     * @param \Exception $previous The previous exception
+     */
+    public function __construct($message = null, $code = 0, Exception $previous = null)
+    {
+        if ($message) {
+            $message = sprintf($this->messageTemplate, $message);
+        }
+        return parent::__construct($message, $code, $previous);
+    }
+}

tests/Session/BaseTest.php

@@ -122,4 +122,22 @@ public function testParticipateInvalidForcedAlternative()
 
         $base->participate('experiment', ['one', 'two']);
     }
+
+    /**
+     * Verify what happens with a bad experiment name
+     *
+     * @expectedException \SeatGeek\Sixpack\Session\Exception\InvalidExperimentNameException
+     * @expectedExceptionMessage The experiement name "experiments; the final frontier" is invalid
+     */
+    public function testParticipateInvalidExperimentName()
+    {
+        $_GET['sixpack-force-experiment'] = 'not configured';
+
+        $base = $this->getMockBuilder('SeatGeek\Sixpack\Session\Base')
+            ->disableOriginalConstructor()
+            ->setMethods(['nothing'])
+            ->getMock();
+
+        $base->participate('experiments; the final frontier', ['one', 'two']);
+    }
 }