feature #6273 [PHPUnit bridge] Add documentation for the component (t…

…heofidry)

This PR was submitted for the 2.3 branch but it was merged into the 2.7 branch instead (closes #6273).

Discussion
----------

[PHPUnit bridge] Add documentation for the component

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #5059

First draft of the doc. I'm not hyper familiar with the component so I may have overlooked a feature. Also I kind of find the name off: *PHPUnit Bridge*, it's not about a bridge, it's about deprecation. Bridge is the technical solution to bring it, it does not reflect what the component does.

Commits
-------

6a1d886 [PHPUnit bridge] Add documentation for the component

components/index.rst

@@ -23,6 +23,7 @@ The Components
     http_kernel/index
     intl
     options_resolver
+    phpunit_bridge
     process
     property_access/index
     routing/index

components/map.rst.inc

@@ -5,7 +5,7 @@
   * :doc:`/components/asset/introduction`
 
 * :doc:`/components/browser_kit/index`
-  
+
   * :doc:`/components/browser_kit/introduction`
 
 * :doc:`/components/class_loader/index`
@@ -115,6 +115,10 @@
 
   * :doc:`/components/options_resolver`
 
+* **PHPUnitBridge**
+
+  * :doc:`/components/phpunit_bridge`
+
 * **Process**
 
   * :doc:`/components/process`

components/phpunit_bridge.rst

@@ -0,0 +1,242 @@
+.. index::
+   single: PHPUnitBridge
+   single: Components; PHPUnitBridge
+
+The PHPUnit Bridge
+==================
+
+    The PHPUnit Bridge provides utilities to report legacy tests and usage of
+    deprecated code and a helper for time-sensitive tests.
+
+It comes with the following features:
+
+* Forces the tests to use a consistent locale (``C``);
+
+* Auto-register ``class_exists`` to load Doctrine annotations (when used);
+
+* It displays the whole list of deprecated features used in the application;
+
+* Displays the stack trace of a deprecation on-demand;
+
+* Provides a `ClockMock` mock class for time-sensitive tests.
+
+Installation
+------------
+
+You can install the component in 2 different ways:
+
+* :doc:`Install it via Composer </components/using_components>`
+  (``symfony/phpunit-bridge`` on `Packagist`_); as a dev dependency;
+
+* Use the official Git repository (https://github.com/symfony/phpunit-bridge).
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+Once the component installed, it automatically registers a
+`PHPUnit event listener`_ which in turn registers a `PHP error handler`_
+called ``DeprecationErrorHandler``. After running your PHPUnit tests, you will
+get a report similar to this one:
+
+.. image:: /images/components/phpunit_bridge/report.png
+
+The summary includes:
+
+**Unsilenced**
+    Reports deprecation notices that were triggered without the recommended
+    `@-silencing operator`_.
+
+**Legacy**
+    Deprecation notices denote tests that explicitly test some legacy features.
+
+**Remaining/Other**
+    Deprecation notices are all other (non-legacy) notices, grouped by message,
+    test class and method.
+
+Trigger Deprecation Notices
+---------------------------
+
+Deprecation notices can be triggered by using::
+
+    @trigger_error('Your deprecation message', E_USER_DEPRECATED);
+
+Without the `@-silencing operator`_, users would need to opt-out from deprecation
+notices. Silencing by default swaps this behavior and allows users to opt-in
+when they are ready to cope with them (by adding a custom error handler like the
+one provided by this bridge). When not silenced, deprecation notices will appear
+in the **Unsilenced** section of the deprecation report.
+
+Mark Tests as Legacy
+--------------------
+
+There are four ways to mark a test as legacy:
+
+* (**Recommended**) Add the ``@group legacy`` annotation to its class or method;
+
+* Make its class start with the ``Legacy`` prefix;
+
+* Make its method start with ``testLegacy``;
+
+* Make its data provider start with ``provideLegacy`` or ``getLegacy``.
+
+Configuration
+-------------
+
+In case you need to inspect the stack trace of a particular deprecation
+triggered by your unit tests, you can set the ``SYMFONY_DEPRECATIONS_HELPER``
+`environment variable`_ to a regular expression that matches this deprecation's
+message, enclosed with ``/``. For example, with:
+
+.. code-block:: xml
+
+    <!-- http://phpunit.de/manual/4.1/en/appendixes.configuration.html -->
+    <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+             xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.1/phpunit.xsd"
+    >
+
+        <!-- ... -->
+
+        <php>
+            <server name="KERNEL_DIR" value="app/" />
+            <env name="SYMFONY_DEPRECATIONS_HELPER" value="/foobar/" />
+        </php>
+    </phpunit>
+
+PHPUnit_ will stop your test suite once a deprecation notice is triggered whose
+message contains the ``"foobar"`` string.
+
+Making Tests Fail
+-----------------
+
+By default, any non-legacy-tagged or any non-`@-silenced`_ deprecation notices will
+make tests fail. Alternatively, setting ``SYMFONY_DEPRECATIONS_HELPER`` to an
+arbitrary value (ex: ``320``) will make the tests fails only if a higher number
+of deprecation notices is reached (``0`` is the default value). You can also set
+the value ``"weak"`` which will make the bridge ignore any deprecation notices.
+This is useful to projects that must use deprecated interfaces for backward
+compatibility reasons.
+
+Time-sensitive Tests
+--------------------
+
+Use Case
+~~~~~~~~
+
+If you have this kind of time-related tests::
+
+    use Symfony\Component\Stopwatch\Stopwatch;
+
+    class MyTest extends \PHPUnit_Framework_TestCase
+    {
+        public function testSomething()
+        {
+            $stopwatch = new Stopwatch();
+
+            $stopwatch->start();
+            sleep(10);
+            $duration = $stopwatch->stop();
+
+            $this->assertEquals(10, $duration);
+        }
+    }
+
+You used the :doc:`Symfony Stopwatch Component </components/stopwatch>` to
+calculate the duration time of your process, here 10 seconds. However, depending
+on the load of the server your the processes running on your local machine, the
+``$duration`` could for example be `10.000023s` instead of `10s`.
+
+This kind of tests are called transient tests: they are failing randomly
+depending on spurious and external circumstances. They are often cause trouble
+when using public continuous integration services like `Travis CI`_.
+
+Clock Mocking
+~~~~~~~~~~~~~
+
+The ``ClockMock`` class provided by this bridge allows you to mock the PHP's
+built-in time functions ``time()``, ``microtime()``, ``sleep()`` and
+``usleep()``.
+
+To use the ``ClockMock`` class in your test, you can:
+
+* (**Recommended**) Add the ``@group time-sensitive`` annotation to its class or
+  method;
+
+* Register it manually by calling ``\Symfony\Bridge\PhpUnit\ClockMock::register(true)``
+  (before the test) and ``Symfony\Bridge\PhpUnit\ClockMock::register(false)``
+  (after the test).
+
+As a result, the following is guarenteed to work and is no longer a transient
+test:
+
+.. code-block:: php
+
+    use Symfony\Component\Stopwatch\Stopwatch;
+
+    /**
+     * @group time-sensitive
+     */
+    class MyTest extends \PHPUnit_Framework_TestCase
+    {
+        public function testSomething()
+        {
+            $stopwatch = new Stopwatch();
+
+            $stopwatch->start();
+            sleep(10);
+            $duration = $stopwatch->stop();
+
+            $this->assertEquals(10, $duration);
+        }
+    }
+
+And that's all!
+
+An added bonus of using the ``ClockMock`` class is that time passes instantly.
+Using PHP's ``sleep(10)`` will make your test wait for 10 actual seconds (more
+or less). In contrast, the ``ClockMock`` class advances the internal clock the
+given number of seconds without actually waiting that time, so your test will
+execute 10 seconds faster.
+
+Troubleshooting
+~~~~~~~~~~~~~~~
+
+The ``@group time-sensitive`` works "by convention" and assumes that the
+namespace of the tested class can be obtained just by removing the ``\Tests\``
+part from the test namespace. I.e. that if the your test case fully-qualified
+class name (FQCN) is ``App\Tests\Watch\DummyWatchTest``, it assumes the tested
+class FQCN is ``App\Watch\DummyWatch``.
+
+If this convention doesn't work for your application, you can also configure
+the mocked namespaces in the `phpunit.xml` file, as done for example in the
+:doc:`HttpKernel Component </components/http_kernel/introduction>`:
+
+.. code-block:: xml
+
+    <!-- http://phpunit.de/manual/4.1/en/appendixes.configuration.html -->
+    <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+             xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.1/phpunit.xsd"
+    >
+
+        <!-- ... -->
+
+        <listeners>
+            <listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener">
+                <arguments>
+                    <array>
+                        <element><string>Symfony\Component\HttpFoundation</string></element>
+                    </array>
+                </arguments>
+            </listener>
+        </listeners>
+    </phpunit>
+
+.. _PHPUnit: https://phpunit.de
+.. _`PHPUnit event listener`: https://phpunit.de/manual/current/en/extending-phpunit.html#extending-phpunit.PHPUnit_Framework_TestListener
+.. _`PHP error handler`: http://php.net/manual/en/book.errorfunc.php
+.. _`environment variable`: https://phpunit.de/manual/current/en/appendixes.configuration.html#appendixes.configuration.php-ini-constants-variables
+.. _Packagist: https://packagist.org/packages/symfony/phpunit-bridge
+.. _`@-silencing operator`: http://php.net/manual/en/language.operators.errorcontrol.php
+.. _`@-silenced`: http://php.net/manual/en/language.operators.errorcontrol.php
+.. _`Travis CI`: https://travis-ci.com/