minor symfony#12798 It's needed to change the returned string in testControllerResponse (demyanovs)

This PR was submitted for the master branch but it was merged into the 4.3 branch instead (closes symfony#12798).

Discussion
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It's needed to change the returned string in testControllerResponse

Following the documentation, we check the Calendar application and get the string "Yep, this is a leap year!" instead of "Hello Fabien".

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Commits
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8f96598 It's needed to change the returned string

Author: javiereguiluz

create_framework/unit_testing.rst

@@ -183,7 +183,7 @@ Response::
         $response = $framework->handle(new Request());
 
         $this->assertEquals(200, $response->getStatusCode());
-        $this->assertContains('Hello Fabien', $response->getContent());
+        $this->assertContains('Yep, this is a leap year!', $response->getContent());
     }
 
 In this test, we simulate a route that matches and returns a simple