minor #21357 [Console] Mention how to test a multiline question’s answer (MatTheCat)

This PR was submitted for the 7.3 branch but it was merged into the 6.4 branch instead.

Discussion
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[Console] Mention how to test a multiline question’s answer

symfony/symfony#61690 follow-up

Commits
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4545c5a [Console] Mention how to test a multiline question’s answer

Author: javiereguiluz

components/console/helpers/questionhelper.rst

@@ -545,6 +545,14 @@ from the command line, you need to set the inputs that the command expects::
         // additional input saying "yes" will work
         $commandTester->setInputs(['yes']);
 
+        // Answers to multiline questions need to be suffixed by
+        // an end-of-transmission control character
+        $commandTester->setInputs([<<<INPUT
+            First line
+            Second line
+            \x04
+            INPUT]);
+
         $commandTester->execute(['command' => $command->getName()]);
 
         // $this->assertRegExp('/.../', $commandTester->getDisplay());