minor #7587 Added note about using the Validator TypeTestCase in form unit testing (pierredup, javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Added note about using the Validator TypeTestCase in form unit testing

This update ads the usage of the validator TypeTestCase class to use for testing when validation is required.

Commits
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c495b92 Readded a blank line
ff1bd8e Reverted some changes
f0887ae Remove section about forms using validation
6fda2df Removed extra class
cf0f9e6 Update fomr testing sentence
070b2c0 Renamed TestedTypeTests to TestedTypeTest
d17821a Fix heading underlining
d4979eb Fix typos
3e6dc19 Add docs about the validator TypeTestCase class

Author: javiereguiluz

form/unit_testing.rst

@@ -125,7 +125,7 @@ To create your form correctly, you need to make the type available to the
 form factory in your test. The easiest way is to register it manually
 before creating the parent form using the ``PreloadedExtension`` class::
 
-    // src/AppBundle/Tests/Form/Type/TestedTypeTests.php
+    // src/AppBundle/Tests/Form/Type/TestedTypeTest.php
     namespace AppBundle\Tests\Form\Type;
 
     use AppBundle\Form\Type\TestedType;
@@ -170,7 +170,7 @@ will be raised if you try to test a class that depends on other extensions.
 The :method:`Symfony\\Component\\Form\\Test\\TypeTestCase::getExtensions` method
 allows you to return a list of extensions to register::
 
-    // src/AppBundle/Tests/Form/Type/TestedTypeTests.php
+    // src/AppBundle/Tests/Form/Type/TestedTypeTest.php
     namespace AppBundle\Tests\Form\Type;
 
     use AppBundle\Form\Type\TestedType;
@@ -211,7 +211,7 @@ Testing against Different Sets of Data
 If you are not familiar yet with PHPUnit's `data providers`_, this might be
 a good opportunity to use them::
 
-    // src/AppBundle/Tests/Form/Type/TestedTypeTests.php
+    // src/AppBundle/Tests/Form/Type/TestedTypeTest.php
     namespace AppBundle\Tests\Form\Type;
 
     use AppBundle\Form\Type\TestedType;