Tests: Fix unit tests for wpcom (#21649)

* Tests: Collect mocked functions in

Since we're starting to accumulate more mocked functions, let's collect them all in a single file.

* [not verified] Create fix-jetpack-unit-wpcom

* Set subscriber count from within test

wpcom clears all caches at the end of `setUp()` so that test always fails.

Also removes the file inclusion as noted by @anomiex.

* Fix package typo

Props @anomiex.

* Add subscriptions test to multisite env

See Automattic/jetpack#21649 (comment)

* Account for difference in folder structure for multisite tests

* Update file structure

Co-authored-by: Brad Jorsch <anomiex@users.noreply.github.com>

* Don't rely on unrelated tests to include dependencies

Props @anomiex

Co-authored-by: Brad Jorsch <anomiex@users.noreply.github.com>

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/1473348538

CHANGELOG.md

@@ -11,6 +11,7 @@ This is an alpha version! The changes listed here are not final.
 
 ### Other changes <!-- Non-user-facing changes go here. This section will not be copied to readme.txt. -->
 - Adding My Jetpack
+- Update phpunit tests so they can be executed again on wpcom without fatal errors.
 
 ## 10.4-a.5 - 2021-11-16
 ### Enhancements