Add a (at least empty) test

Here is a patch with a simple test, so the testbot lets us pass.

Thanks so much! I'm not super familiar with unit tests, so I'll defer to others to review.

Looks pretty good, but...

+++ b/tests/src/Unit/FetchManagerTest.php
@@ -0,0 +1,105 @@
+      $stream_wrapper_manager = $this->getMockBuilder('Drupal\Core\StreamWrapper\StreamWrapperManagerInterface')
...
+      $this->logger = $this->getMockBuilder('Psr\Log\LoggerInterface')
...
+      $this->fileSystem = new FileSystem($stream_wrapper_manager, $settings, $this->logger);
+      $this->fetchManager = new FetchManager($this->client, $this->fileSystem, $this->logger);
...
+  if (!function_exists('file_default_scheme')) {

If you find yourself doing a lot of mocking of services, you should probably convert to a KernelTestBase test. That will do a lot of the work for you in terms of setting up services and loading modules (but not enabling them).

Thanks Mile23. I will refactor as a kernel test .

Here is a patch with the test re-written as a kernel test instead of a unit test.

Please review. Thanks!

That's indeed a lot simpler. Thanks for posting it.

You are welcome!

@mile23 can you review again? Does this seem good to you?

I disagree on the service mocking argument because if there are interfaces mock away and you can better assert your excepted behaviors with fewer complications.

That said, the config and file system complications make this better suited for the kernel test. LGTM.

Thanks for the reviews, neclimdul and mile23, and for the patch here, philltran.

Thanks neclimdul and mile23 for reviewing and for the pointers.