21 May 2024 Leave a comment Tech-Help
When working with pytest and the parametrize decorator, there are occasions where you may want to run just a single test case out of a set of parameterized tests. This can be especially useful when debugging or focusing on a specific scenario. Below, we outline effective methods to achieve this.
Using the -k Flag
One straightforward method is to use the -k flag. This flag allows you to filter tests that match a specified string expression. Pytest names each test case using the convention:
test_name['-' separated test inputs]
For example, if you have a test named test_my_feature with parameters value_1 and value_2, you can run this particular test case by using the following command:
pytest -k 'test_my_feature[value_1-value_2]'Alternatively, you can use:
pytest -k test_my_feature\\[value_1-value_2\\]Note that you need to escape the square brackets.
Using –collect-only
Another method involves using the --collect-only flag to list all tests without executing them. This can help you identify the exact name of the test you wish to run. Here’s how:
pytest --collect-only -qAfter identifying the test name, you can run the specific test by using:
pytest test_file_name.py::test_my_feature[value_1-value_2]Be sure to use quotes if there are spaces in the identifier.
Limiting the Number of Test Runs
If you have parameterized tests that take a long time to run, you can limit the number of test runs by adding custom options to your conftest.py file. This approach can be particularly useful for running a subset of tests for quick feedback. Add the following code to your conftest.py:
def pytest_addoption(parser):
parser.addoption(
"--limit",
action="store",
default=-1,
type=int,
help="Maximum number of permutations of parametrized tests to run",
)
def pytest_collection_modifyitems(session, config, items):
def get_base_name(test_name):
try:
return test_name[: test_name.index("[")]
except ValueError:
return test_name
limit = config.getoption("--limit")
if limit >= 0:
tests_by_name = {item.name: item for item in items}
test_base_names = set(get_base_name(name) for name in tests_by_name.keys())
tests_to_run = []
for base_name in test_base_names:
to_skip = [t for n, t in tests_by_name.items() if base_name in n][limit:]
for t in to_skip:
t.add_marker("skip")Conclusion
Running a single test case in a set of parameterized tests is straightforward with the right commands and configurations. By using the -k flag, the --collect-only option, or limiting the number of test runs, you can efficiently focus on specific test scenarios.
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