minor #13050 [Testing] Documented the changes in MailerAssertionsTrait (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #13050).

Discussion
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[Testing] Documented the changes in MailerAssertionsTrait

Fixes #13044.

Commits
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5b0590e [Testing] Documented the changes in MailerAssertionsTrait

Author: javiereguiluz

testing/functional_tests_assertions.rst

@@ -18,17 +18,17 @@ This is the same example using the assertions provided by Symfony::
 
     $this->assertResponseRedirects('https://example.com', 301);
 
-.. note::
-
-    These assertions only work if a request has been made with the ``Client``
-    in a test case extending the ``WebTestCase`` class.
-
 Assertions Reference
 ---------------------
 
 Response
 ~~~~~~~~
 
+.. note::
+
+    The following assertions only work if a request has been made with the
+    ``Client`` in a test case extending the ``WebTestCase`` class.
+
 - ``assertResponseIsSuccessful()``
 - ``assertResponseStatusCodeSame()``
 - ``assertResponseRedirects()``
@@ -43,12 +43,22 @@ Response
 Request
 ~~~~~~~
 
+.. note::
+
+    The following assertions only work if a request has been made with the
+    ``Client`` in a test case extending the ``WebTestCase`` class.
+
 - ``assertRequestAttributeValueSame()``
 - ``assertRouteSame()``
 
 Browser
 ~~~~~~~
 
+.. note::
+
+    The following assertions only work if a request has been made with the
+    ``Client`` in a test case extending the ``WebTestCase`` class.
+
 - ``assertBrowserHasCookie()``
 - ``assertBrowserNotHasCookie()``
 - ``assertBrowserCookieValueSame()``
@@ -58,8 +68,9 @@ Crawler
 
 .. note::
 
-    You cannot use the :doc:`Crawler </components/dom_crawler>` assertions,
-    when using `symfony/panther`_ for end-to-end testing.
+    The following assertions only work if a request has been made with the
+    ``Client`` in a test case extending the ``WebTestCase`` class. In addition,
+    they are not available when using `symfony/panther`_ for end-to-end testing.
 
 - ``assertSelectorExists()``
 - ``assertSelectorNotExists()``
@@ -74,6 +85,11 @@ Crawler
 Mailer
 ~~~~~~
 
+.. versionadded:: 5.1
+
+    Starting from Symfony 5.1, the following assertions no longer require to make
+    a request with the ``Client`` in a test case extending the ``WebTestCase`` class.
+
 - ``assertEmailCount()``
 - ``assertQueuedEmailCount()``
 - ``assertEmailIsQueued()``