There is a lot of redundancy. Let’s not repeat ourselves.
Unfortunately, since we do not install PHPUnit as a project dependency on CI,
it does not use the composer’s PSR-4 autoloader and the tests are unable to find
the `BaseFormatTest` class.
Until we resolve that, let’s load the class explicitly.
We cannot yet switch to namespaces for RSS-Bridge itself but for tests we are not limited by BC.
It does not actually do anything since PHPUnit will search for the test files without the help of the autoloader but it still makes the directory cleaner.
