[#125] Adds expectation to whoops prophecy

- The Whoops runtime should now be injected with a pretty page handler,
  per #125.

Author: weierophinney

test/WhoopsErrorHandlerTest.php

@@ -45,12 +45,13 @@ public function testExceptionErrorPreparesPageHandlerAndInvokesWhoops()
     {
         $exception = new Exception('Boom!');
 
-        $whoops = $this->getWhoops();
-        $whoops->handleException($exception)->willReturn('Whoops content');
-
         $pageHandler = $this->getPrettyPageHandler();
         $pageHandler->addDataTable('Expressive Application Request', Argument::type('array'))->shouldBeCalled();
 
+        $whoops = $this->getWhoops();
+        $whoops->handleException($exception)->willReturn('Whoops content');
+        $whoops->pushHandler(Argument::type(PrettyPageHandler::class))->shouldBeCalled();
+
         $handler = new WhoopsErrorHandler($whoops->reveal(), $pageHandler->reveal());
 
         $stream    = $this->prophesize(StreamInterface::class);