minor #15971 [FrameworkBundle] 15751 add documentation for assertThatForClient (JohJohan)

This PR was merged into the 5.4 branch.

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[FrameworkBundle] 15751 add documentation for assertThatForClient

Fixes #15751

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cc46616 [FrameworkBundle] 15751 add documentation for assertThatForClient

Author: javiereguiluz

testing.rst

@@ -922,6 +922,8 @@ Browser Assertions
 ``assertBrowserCookieValueSame(string $name, string $expectedValue, string $path = '/', string $domain = null, string $message = '')``
     Asserts the given cookie in the test Client is set to the expected
     value.
+``assertThatForClient(Constraint $constraint, string $message = '')``
+    Asserts the given Constraint in Client.
 
 Crawler Assertions
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