How to migrate pytest to bazel py_test? - pytest

Question

I want to convert our integration pytests over to bazel, but it doesn't seem to actually run nor produce the junitxml output I'm expecting:
ARGS = [
"--verbose",
"--json-report",
"--junit-xml=junit.xml",
]
py_test(
name = "test_something",
srcs = ["test_something.py"],
args = ARGS,
tags = [
"yourit",
],
deps = [
requirement("pytest"),
requirement("pytest-json-report"),
":lib",
],
)
There is a similar question here: How do I use pytest with bazel?. But it didn't cover the multitude of issues I ran into.

Answer 1

So there were multiple things to address in order to make bazel's py_test work with pytest.
Of course you need the pytest dependency requirement("pytest") added.
The pytest files require a hook being added (note that the args are passed as well sys.argv[1:], so py_test args can be passed on to the pytest file):
if __name__ == "__main__":
sys.exit(pytest.main(\[__file__\] + sys.argv\[1:\]))
Since our pytests are trying to access the host network, we need to tell bazel to allow network traffic outside the sandbox by adding a requires-network tag.
The host network is local, so we need to make sure the test runs locally by adding the local tag.
Bazel py_test will create junitxml under bazel-testlogs, but it only shows if py_test rule passed or failed. To get more granular junitxml results, we need to tell pytest how to overwrite bazel's py_test results using XML_OUTPUT_FILE environment variable. Note the $$ is needed to prevent variable expansion. See https://docs.bazel.build/versions/main/test-encyclopedia.html and https://github.com/bazelbuild/bazel/blob/master/tools/test/test-setup.sh#L67 for more info.
Attempts to write json report output to bazel-testlogs using TEST_UNDECLARED_OUTPUTS_DIR environment variable didn't work. The report is still written, but inside bazel-out. There might be a way to scoop up those files, but solving that problem was not a priority.
Note that the ARGS is used to keep it DRY (don't repeat yourself). We use the same arguments across multiple py_test rules.
So the BUILD now looks like this:
ARGS = [
"--verbose",
"--json-report",
"--junit-xml=$$XML_OUTPUT_FILE",
]
py_test(
name = "test_something",
srcs = ["test_something.py"],
args = ARGS,
tags = [
"local",
"requires-network",
"yourit",
],
deps = [
requirement("pytest"),
requirement("pytest-json-report"),
":lib",
],
)