Invalid tests in MigrateSourceTest

Problem/Motivation

There are two invalid tests in core/modules/migrate/tests/src/Unit/MigrateSourceTest.php. Both testCount() and testCountCacheKey() contain the following code:

    // Mock the cache to validate set() receives appropriate arguments.
    $container = new ContainerBuilder();
    $cache = $this->createMock(CacheBackendInterface::class);
    $cache->expects($this->any())->method('set')
      ->with($this->isString(), $this->isInt(), $this->isInt());
    $container->set('cache.migrate', $cache);
    \Drupal::setContainer($container);

Per the comment at the top, the intent is to validate that a cache entry is set with particular arguments. But the expectation for the set() function is any(), which implicitly means that it's valid if set() is never called. As it turns out, that's what happens.

The problem is that the functions call getSource() (in one case multiple times) which creates a container with a different cache service. This overrides what the test functions are trying to do.

This was discovered in the course of working on #3569422: Convert expectation-less test mocks to stubs - Migrate modules where calls to any() are being removed.

Steps to reproduce

Change the any() to atLeastOnce() and run the tests. The tests will throw errors because set() is never called.

Proposed resolution

• getSource() will continue to set a default stubbed cache service.
• The functions that want to validate a specific interaction with the cache will now override the service with a mock object.
• Move the assertions for checking that the cache is being set to the right place within the test functions.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet