[Tests] Added ClockMock to make time-sensitive tests more robust

[mnocon]

Question	Answer
JIRA issue	n/a
Type	Improvement in tests
Target version	1.0, needs to be adapted in 2.1 and master (1)
BC breaks	no
Doc needed	no

Failing build: https://travis-ci.org/github/ezsystems/ezplatform-http-cache/jobs/725689032

1) eZ\Publish\Core\MVC\Symfony\Cache\Tests\LocalPurgeClientTest::testPurge

Expectation failed for method name is equal to 'purgeByRequest' when invoked 1 time(s)

Parameter 0 for invocation EzSystems\PlatformHttpCacheBundle\RequestAwarePurger::purgeByRequest(Symfony\Component\HttpFoundation\Request Object (...)) does not match expected value.

Failed asserting that two objects are equal.

--- Expected

+++ Actual

@@ @@

             'SCRIPT_NAME' => ''
             'SCRIPT_FILENAME' => ''
             'SERVER_PROTOCOL' => 'HTTP/1.1'
-            'REQUEST_TIME' => 1599682188
+            'REQUEST_TIME' => 1599682189
             'PATH_INFO' => ''
             'REQUEST_METHOD' => 'PURGE'
             'REQUEST_URI' => '/'

Request::create uses time() method under the hood to set the REQUEST_TIME header. By using the ClockMock (as described in https://symfony.com/doc/3.4/components/phpunit_bridge.html#time-sensitive-tests) we can make sure that the time call in Request class is mocked and we're not hit by this issue again

There are 2 deprecation warnings in current tests:

OK, but incomplete, skipped, or risky tests!
Tests: 3385, Assertions: 3881, Skipped: 162, Incomplete: 4.

Remaining direct deprecation notices (1)

  1x: The eZ\Publish\Core\SignalSlot\Signal\ContentService\RemoveTranslationSignal is deprecated since 6.13 and will be removed in 7.0. Use eZ\Publish\Core\SignalSlot\Signal\ContentService\DeleteTranslationSignal instead
    1x in RemoveTranslationSlotTest::getReceivedSignals from EzSystems\PlatformHttpCacheBundle\Tests\SignalSlot

Other deprecation notices (1)

  1x: The eZ\Publish\Core\Repository\Repository::getCurrentUser method is deprecated (since 6.6, to be removed. Use PermissionResolver::getCurrentUserReference() instead.  Get current user.  Loads the full user object if not already loaded, if you only need to know user id use {@see getCurrentUserReference()}).
    1x in RoleIdentifyTest::testSetIdentity from EzSystems\PlatformHttpCacheBundle\Tests\ContextProvider

I've disabled them as described in https://symfony.com/doc/3.4/components/phpunit_bridge.html#disabling-the-deprecation-helper, because I don't want to introduce too many changes here.

(1) In 2.1 and master the whole request is not compared:
https://github.com/ezsystems/ezplatform-http-cache/blob/2.1/tests/PurgeClient/LocalPurgeClientTest.php
so the test is not time-sensitive, but I think we can keep the dependency for future usages.

TODO:

• Implement feature / fix a bug.
• Implement tests + specs and passing ($ composer test)
• Fix new code according to Coding Standards ($ composer fix-cs).
• Ask for Code Review.