[VarDumper] Add doc for assertDump* assertions

Author: nicolas-grekas

components/var_dumper/introduction.rst

@@ -10,6 +10,7 @@ The VarDumper Component
     function that you can use instead of :phpfunction:`var_dump`.
 
 .. versionadded:: 2.6
+
     The VarDumper component was introduced in Symfony 2.6.
 
 Installation
@@ -73,6 +74,33 @@ current PHP SAPI:
     #. From time to time, run ``composer global update`` to have the latest
        bug fixes.
 
+
+
+Using the VarDumper Component in Your PHPUnit Test Suite
+--------------------------------------------------------
+
+The VarDumper component provides
+:class:`a trait <Symfony\\Component\\VarDumper\\Test\\VarDumperTestTrait>`
+that can help writting some of your tests for PHPUnit.
+By adding::
+
+    use \Symfony\Component\VarDumper\Test\VarDumperTestTrait;
+
+at the beginning of your test class declaration, you'll gain two new assertions:
+
+:method:`Symfony\\Component\\VarDumper\\Test\\VarDumperTestTrait::assertDumpEquals`
+    verifies that the dump of the variable given as the second argument matches
+    the expected dump provided as a string in the first argument.
+
+:method:`Symfony\\Component\\VarDumper\\Test\\VarDumperTestTrait::assertDumpMatchesFormat`
+    is like the previous method but accepts placeholders in the expected dump,
+    based on the ``assertStringMatchesFormat`` method provided by PHPUnit.
+
+.. versionadded:: 2.7
+
+    The :class:`Symfony\\Component\\VarDumper\\Test\\VarDumperTestTrait` was
+    introduced in Symfony 2.7.
+
 DebugBundle and Twig Integration
 --------------------------------