pytest - simple powerful testing with Python

Options you will use

-v

One line per test with PASSED/FAILED.

-q

Quiet: dots only.

-x

Stop at the first failure.

-k EXPR

Only run tests whose name contains EXPR ("not EXPR" to exclude).

-s

Do not capture output: print() shows up live (--capture=no).

--maxfail=N

Stop after N failures.

-m MARKEXPR

Only run tests matching the marker expression.

--lf, --last-failed

Rerun only the tests that failed last time.

--tb=STYLE

Traceback style: auto, long, short, line, no.

-r CHARS

Short summary of the given outcomes: f failed, E error, s skipped, a all but passes.

--junitxml=PATH

Write a JUnit XML report (what CI dashboards read).

--cov=PATH

Measure coverage of PATH (pytest-cov).

Examples

$ pytest

Collect test_*.py / _test.py under the current directory and run every test_ function.

$ pytest test_checks.py::test_timeout -v

Run one test.

Gotchas

• Plain assert statements are rewritten so a failure shows the values: "assert 1 == 2" and "+ where 1 = exit_code_for('DOWN')".
• Fixtures are functions decorated with @pytest.fixture; a test asks for one by naming it as a parameter. Built in: tmp_path (a fresh directory per test), monkeypatch (setattr/setenv, undone after the test), capsys (captured output).
• Exit codes: 0 all passed, 1 some failed, 2 interrupted (e.g. a collection error), 5 no tests collected.