Description

Fixes #880

Type of change

No scenario necessary, this is only changing testing code.

Update the tests base to use the v3 of our PHPUnit library, to bring it up to par with our other plugins.

wp-media/phpunit: 3

[x] I validated all the Acceptance Criteria. If possible, provide screenshots or videos.
[x] I triggered all changed lines of code at least once without new errors/warnings/notices.
[x] I implemented built-in tests to cover the new/changed code.

[x] I wrote a self-explanatory code about what it does.
[x] I protected entry points against unexpected inputs.
[x] I did not introduce unnecessary complexity.
[x] Output messages (errors, notices, logs) are explicit enough for users to understand the issue and are actionnable.