Make all tests discoverable on Linux

[glbrntt]

Motivation:

Test discovery on Linux relies on source code analysis. Tests in
subclasses which do not explicitly redeclare each test are missed. As a
result, a number of tests are not run on Linux.

Modifications:

• Explicitly redeclare tests in subclasses.

Result:

• Resolves Several test cases do not run on Linux #1392

[glbrntt]

I diffed the output of swift test --list-tests on macOS and linux to determine which tests were missing.

I was hoping we might be able to use swift package dump-package to analyse functions in test modules and diff them with the list of tests (so we could check if any tests are missing as part of CI) but dump-package does not include test targets.

[simonjbeaumont]

OOI, what's going to stop this from diverging when a new test is added to the base class? Do you think it's worth adding a CI check for the diff you performed manually for this PR?

[Lukasa]

I'm +1 with @simonjbeaumont: I'd love to see a tool written for this that we can reuse on our other repos.

[glbrntt]

Oh I totally agree, a tool would be great and that's what I looked at doing first:

I was hoping we might be able to use swift package dump-package to analyse functions in test modules and diff them with the list of tests (so we could check if any tests are missing as part of CI) but dump-package does not include test targets.

If you have any other ideas I'm all ears!

[glbrntt]

One option is parsing all the test files and attempting to build up a graph of test classes and analysing them that way. Not ideal but probably workable.