Generate lockfile for using pytest

[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 configures pants so it can use pytest when running the test goal. However, our test suite does not completely support pytest. Getting this lockfile in is a prerequisite to being able to running tests with it.

pytest version

I opted to go with the version of pytest that pants has pinned by default.

st2/pants.toml

Lines 147 to 149 in 43e2a1d

	[pytest]
	lockfile = "lockfiles/pytest.lock"
	version = "pytest==7.0.1" # copied from https://www.pantsbuild.org/v2.14/docs/reference-pytest#version

pytest plugins

By default pants includes pytest-cov and pytest-xdist plugins for pytest. We get those too because I'm using extra_requirements.add; if I used extra_requirements it would overwrite those.

st2/pants.toml

Line 150 in 43e2a1d

extra_requirements.add = [

We already install pytest-benchmark[histogram] for our tests in st2common/benchmarks, so I copied that pinned version as is:

st2/test-requirements.txt

Line 41 in 43e2a1d

pytest-benchmark[histogram]==3.4.1

st2/pants.toml

Line 151 in 43e2a1d

"pytest-benchmark[histogram]==3.4.1", # used for st2common/benchmarks

Then I added several other plugins, some of which I left commented (we can check them out later when we do more with pytest):

st2/pants.toml

Lines 152 to 158 in 43e2a1d

	#"pytest-timer[colorama]", # report test timing (--with-timer ala nose-timer)
	"pytest-icdiff", # make diff output easier to read
	"pygments", # highlight code in tracebacks
	# other possible plugins
	#"pytest-timeout", # time limit on tests
	#"pytest-mock", # more convenient mocking

This is partially based on recommendations in the pants docs. See: https://www.pantsbuild.org/docs/python-test-goal
These plugins have made what I've done with pytest so far, more enjoyable.

pytest args

As recommended at https://www.pantsbuild.org/docs/python-test-goal#controlling-output, I dropped the pytest header. Pants runs each test file separately to help with caching, so that header becomes very annoying and repetitive.

st2/pants.toml

Lines 164 to 166 in 43e2a1d

	args = [
	"--no-header", # don't print pytest version for every tested file
	]

parallel tests with mongo

This line of the config builds on #5707, so that pants can safely run tests that use mongo in parallel.

st2/pants.toml

Line 167 in 43e2a1d

execution_slot_var = "ST2TESTS_PARALLEL_SLOT"

see:

• https://www.pantsbuild.org/docs/reference-pytest#execution_slot_var
• https://www.pantsbuild.org/docs/troubleshooting#controlling-test-parallelism

[Eric-Arellano]

You won't be able to use some Pants features with these commented out

[cognifloyd]

This serves as documentation because I'm using extra_requirements.add