This is take #2 and must be processed after take #1 (MDL-82207) is integrated.

As commented in the parent (MDL-82142) of this, there are a lot of incorrect coverage annotations in codebase, all them are reported as warnings when running tests with coverage options enabled. Example:

1) core\dml_read_slave_test::test_transaction

"@covers ::can_use_readonly" is invalid

This issue (the 2nd in a series) is about to, gradually go fixing all those warnings, towards clean (without warnings) runs. Of course, they also will lead to better (more accurate) code coverage information.

The basic idea to follow is:

• When possible, switch to simpler (and recommended) class coverage. Change from current coverage.
• When there are multiple classes involved, try the best applying default class coverage and individual method coverage. Observing the original coverage.

And that's it. As said, this problem will be fixed along multiple issues, because the current number of warnings is really high (653).

Only for dev versions (4.5dev) in main branch.