pants: use __defaults__ to propogate unit,integration,benchmarks tags on tests

[cognifloyd]

Background

This is another part of introducing pants, as discussed in various TSC meetings.

Related PRs can be found in:

• pantsbuild milestone (which includes PRs since Initialize pantsbuild #5713)
• pantsbuild label (which also includes preparatory PRs that came before adding pantsbuild)

Overview of this PR

This adjusts the BUILD metadata for all of our python_tests targets so that they are tagged with unit, integration, or benchmarks. We can add other tags when/if we find something that will be generally useful.

Once we are able to run tests via pants, pants can use this to select a subset of tests to run. For example:

./pants --tag=benchmarks test

Check out the docs for more powerful examples of how to use tags on the command line.

Relevant pants docs

• Tags: annotating targets

[Eric-Arellano]

FYI there's a gotcha that if you have any python_test targets rather than python_tests, they won't have the tags. That's probably unlikely you'll have that happen, but could. You can avoid the risk by using the key (python_test, python_tests)

[cognifloyd]

FYI there's a gotcha that if you have any python_test targets rather than python_tests, they won't have the tags. That's probably unlikely you'll have that happen, but could. You can avoid the risk by using the key (python_test, python_tests)

Ah yes. Thanks for the pointer. Resolved.