Tests in the ms-files group are never run

[johnbillion]

Tests in the ms-files group are not run by default, but there is also no configuration under which Travis CI (grunt travis:phpunit) or a local test run (grunt test) will run these tests.

Not running ms-files tests. To execute these, use --group ms-files.

A sub-task should be added to the phpunit task in Gruntfile.js to run these tests in the same way that the other excluded test groups such as ajax and external-http are run.

[netweb]

Previously:

• Single Site: #36566 Improve unit tests around multisite's bootstrap, networks, and sites / [37269]
• Multisite: #30256 Create and exclude an area for ms-files.php specific unit tests / [30286]

cc @jeremyfelt As both above tickets were yours do you have any concerns on adding the ms-files group of tests into its own multisite test group for Travis CI?

Testing 41698.diff​ in my local fork:

• PR: ​https://github.com/ntwb/wordpress/pull/5
• Travis CI Build: ​https://travis-ci.org/ntwb/wordpress/builds/267413460

Here's the first job passing with flying colours:

Running "phpunit:ms-files" (phpunit) task
Installing...
Installing network...
Running as multisite...
Not running ajax tests. To execute these, use --group ajax.
Not running external-http tests. To execute these, use --group external-http.
PHPUnit 6.3.0 by Sebastian Bergmann and contributors.
Runtime:       PHP 7.1.8
Configuration: /home/travis/build/ntwb/wordpress/tests/phpunit/multisite.xml
..                                                                  2 / 2 (100%)
You should really fix these slow tests (>150ms)...
 1. 351ms to run Tests_Multisite_MS_Files_Rewriting:test_switch_upload_dir
 2. 313ms to run Tests_Multisite_MS_Files_Rewriting:test_upload_directories_after_multiple_wpmu_delete_blog_with_ms_files
Time: 3.28 seconds, Memory: 88.00MB

[jeremyfelt]

I like this, thanks @netweb. For some reason I remembered the ms-files group being a lot more complicated than those few tests, but it doesn't add much time at all.

[jeremyfelt]

In 41659:

Build/Test Tools: Add ms-files test group to sub-task list.

Previously, the ms-files test group would not run in any automatic configuration. This ensures it is always run as part of the test suite in Travis CI.

Props netweb.
Fixes #41698.