Use a class name that does not actually exist

Using "Foo", a class name that corresponds to no less than 22 fixture
classes, results in the first found "Foo" being loaded when one is
found by the ClassNotFoundFatalErrorHandler error handler, I am not sure
exactly why, but it is not really a big issue because this is a fatal
error handler and execution is not supposed to continue after that.
Except that is very much the case when running the whole test suite
sequentially with ./phpunit . Then we arrive to the DI component test
suite, and a failure happens because \\foo was not supposed to be defined:

> Failed asserting that exception message 'The definition for "\foo" has
> no class attribute, and appears to reference a class or interface in the
> global namespace. Leaving out the "class" attribute is only allowed for
> namespaced classes. Please specify the class attribute explicitly to get
> rid of this error.' contains 'The definition for "\foo" has no class.'.

src/Symfony/Component/Debug/Tests/ErrorHandlerTest.php

@@ -525,7 +525,7 @@ public function testHandleFatalError()
      */
     public function testHandleErrorException()
     {
-        $exception = new \Error("Class 'Foo' not found");
+        $exception = new \Error("Class 'IReallyReallyDoNotExistAnywhereInTheRepositoryISwear' not found");
 
         $handler = new ErrorHandler();
         $handler->setExceptionHandler(function () use (&$args) {
@@ -535,7 +535,7 @@ public function testHandleErrorException()
         $handler->handleException($exception);
 
         $this->assertInstanceOf('Symfony\Component\Debug\Exception\ClassNotFoundException', $args[0]);
-        $this->assertStringStartsWith("Attempted to load class \"Foo\" from the global namespace.\nDid you forget a \"use\" statement", $args[0]->getMessage());
+        $this->assertStringStartsWith("Attempted to load class \"IReallyReallyDoNotExistAnywhereInTheRepositoryISwear\" from the global namespace.\nDid you forget a \"use\" statement", $args[0]->getMessage());
     }
 
     /**