Add the ability to customize the __toString representation of a CallbackToken

spec/Prophecy/Argument/Token/CallbackTokenSpec.php

@@ -39,4 +39,11 @@ function its_string_representation_should_tell_that_its_callback()
     {
         $this->__toString()->shouldReturn('callback()');
     }
+
+    function its_string_representation_can_be_customized()
+    {
+        $this->beConstructedWith('get_class', 'MyCustomTestCase');
+
+        $this->__toString()->shouldReturn('MyCustomTestCase');
+    }
 }

spec/Prophecy/ArgumentSpec.php

@@ -37,6 +37,13 @@ function it_has_a_shortcut_for_callback_token()
         $token->shouldBeAnInstanceOf('Prophecy\Argument\Token\CallbackToken');
     }
 
+    function it_supports_customizing_tostring_representation_for_callback_token()
+    {
+        $token = $this->that('get_class', 'MyCustomTestCase');
+        $token->shouldBeAnInstanceOf('Prophecy\Argument\Token\CallbackToken');
+        $token->__toString()->shouldReturn('MyCustomTestCase');
+    }
+
     function it_has_a_shortcut_for_object_state_token()
     {
         $token = $this->which('getName', 'everzet');

src/Prophecy/Argument.php

@@ -61,12 +61,13 @@ public static function which($methodName, $value)
      * Checks that argument matches provided callback.
      *
      * @param callable $callback
+     * @param string|null $customStringRepresentation Customize the __toString() representation of this token
      *
      * @return Token\CallbackToken
      */
-    public static function that($callback)
+    public static function that($callback, ?string $customStringRepresentation = null)
     {
-        return new Token\CallbackToken($callback);
+        return new Token\CallbackToken($callback, $customStringRepresentation);
     }
 
     /**

src/Prophecy/Argument/Token/CallbackToken.php

@@ -22,14 +22,20 @@ class CallbackToken implements TokenInterface
 {
     private $callback;
 
+    /**
+     * @var string|null
+     */
+    private $customStringRepresentation;
+
     /**
      * Initializes token.
      *
      * @param callable $callback
+     * @param string|null $customStringRepresentation Customize the __toString() representation of this token
      *
      * @throws \Prophecy\Exception\InvalidArgumentException
      */
-    public function __construct($callback)
+    public function __construct($callback, ?string $customStringRepresentation = null)
     {
         if (!is_callable($callback)) {
             throw new InvalidArgumentException(sprintf(
@@ -39,6 +45,7 @@ public function __construct($callback)
         }
 
         $this->callback = $callback;
+        $this->customStringRepresentation = $customStringRepresentation;
     }
 
     /**
@@ -70,6 +77,10 @@ public function isLast()
      */
     public function __toString()
     {
+        if ($this->customStringRepresentation !== null) {
+            return $this->customStringRepresentation;
+        }
+
         return 'callback()';
     }
 }