Running Tests

Running music21 tests and doctests

Every function, method and class needs documentation and at least one passing test. See documentation/source/developerReference/testing.ipynb for the project's own account of testing; this skill covers how to run what is there.

One module: pytest with explicit file paths

uv run pytest music21/abcFormat/__init__.py music21/abcFormat/translate.py

pyproject.toml [tool.pytest.ini_options] already wires up everything:

addopts = ['--doctest-modules', '-p', 'music21.test.pytest_plugin']
doctest_optionflags = ['NORMALIZE_WHITESPACE', 'ELLIPSIS']

So do not pass --doctest-modules yourself -- doctests in every .py are collected automatically, and music21/test/pytest_plugin.py is loaded.

Pass explicit file paths so the in-module Test(unittest.TestCase) classes run too. python_files = ['test_*.py', '*_test.py', 'tests.py'], so for a module that keeps its Test class inside __init__.py / translate.py (e.g. abcFormat), pointing pytest at the directory collects ONLY doctests and silently skips the unittest classes:

• uv run pytest music21/abcFormat/ -> ~43 items (doctests only)
• uv run pytest music21/abcFormat/__init__.py music21/abcFormat/translate.py -> ~82 items (doctests and Test methods)

Modules whose tests live in a tests.py are already picked up by the directory form; the gotcha is specifically a Test class in a non-tests.py file.

A module also runs its own tests directly, via the mainTest call at the foot of each file:

uv run python -m music21.note              # whole module
uv run python music21/note.py testHello    # one test method

Why the plugin matters (and why not to use raw doctest)

music21/test/pytest_plugin.py does three things that make doctests behave as the project intends:

• It runs stripAddresses(example.want, '0x...') (from music21.test.testRunner) on every doctest, so a docstring that hardcodes <music21.abcFormat.ABCHandler object at 0x10b0cf5f8> is normalized and DOES pass. The literal hex address in the docstring is expected and fine.
• It injects the music21.__all__ names plus music21 itself into the doctest namespace, so examples reference meter, key, corpus without importing.
• It keeps only Test classes, dropping TestSlow and TestExternal.

Judge doctest pass/fail through pytest. Do NOT use doctest.testmod(...) or doctest.DocTestSuite(...) directly: that path applies neither the address normalizer nor the namespace injection, so it manufactures false failures on any docstring printing a <... object at 0x...> repr or relying on injected names. An object-address example failing on its own is the tell that doctests were run the wrong way -- rerun through pytest.

Whole suite: the project's runners, not pytest

pytest is for a module. For the whole suite use the runners, and note that a green pytest run does not mean CI will be green -- they gather and order modules differently.

Use multiprocessTest -- it runs on n-1 cores and finishes in about 10 seconds, against roughly 45 for the single-core runner:

uv run python music21/test/multiprocessTest.py

That gap is the whole story when someone is waiting on the answer. Reach for testSingleCoreAll only for what multiprocessTest cannot tell you: it is what GitHub Actions runs, so it is the one to check before a release, when chasing a CI failure that will not reproduce, or on a single-core machine.

uv run python -c 'from music21.test.testSingleCoreAll import ciMain as ci; ci()'

The two runners see slightly different sets of modules -- multiprocessTest walks the package tree for modules reachable from import music21, while testSingleCoreAll gathers module files from disk.

Module order differs between the two runners and again from pytest. multiprocessTest goes in reverse-alphabetical order (with the known-slow modules hoisted to the front on machines with more than 4 cores); testSingleCoreAll re-sorts through common.misc.sortModules, by file mtime, most recently modified first, falling back to reverse-alphabetical when mtimes tie as they do on a fresh clone; pytest walks alphabetically. So a test that depends on module order can pass in one runner and fail in another -- and editing a file locally sorts it to the front of the CI runner, changing the order again.

That makes leaked module-level state the usual cause of "passes alone, fails in the suite." A doctest in duration.py once set humdrum.spineParser.flavors['JRP'] = True and never restored it; flavors is a module-level dict, so every later humdrum test in the same process parsed in the wrong flavor. Under pytest's alphabetical order duration runs before humdrum and the failure appeared; under CI's order it did not.

So: a doctest that mutates module-level state must restore it, using #_DOCS_HIDE so the bookkeeping stays out of the published docs:

>>> saved_JRP_flavor = humdrum.spineParser.flavors['JRP']  #_DOCS_HIDE
>>> humdrum.spineParser.flavors['JRP'] = True
...
>>> humdrum.spineParser.flavors['JRP'] = saved_JRP_flavor  #_DOCS_HIDE

When a test fails only in a full run, re-run it alone. If it then passes, suspect state left behind by an earlier module rather than the test itself.

Speed budget

Aim for about 3 seconds for a module's tests, and never add more than 15 — that is time every contributor waits on every full run. corpus.parse() is nearly always the culprit: build a small stream by hand instead, or parse bwv66.6, which is short and still full of interesting cases (pickup measures, and so on).

Tests that open windows

Nothing in Test or in a doctest may open a window, play audio, or launch another program. Those go in a sibling class, run only when named explicitly:

class TestExternal(unittest.TestCase):
    ...

if __name__ == '__main__':
    import music21
    music21.mainTest(Test, TestExternal)

Because they have those side effects, skip TestExternal when running a file directly.

What tests may do

Exactly one Test(unittest.TestCase) class per module, methods named test.... It must produce no output and require nothing outside the music21 ecosystem. Anything slow goes in a TestSlow sibling, excluded from the normal run like TestExternal.

Regression cases for a bug fix belong in Test, never in a doctest. See the writing-docs skill.

The other gates before a PR or a push

uv run ruff check music21
uv run mypy music21
uv run pylint -j4 music21 --rcfile=.pylintrc   # optional: run only if major refactoring since it was last run.

Coverage is expected to rise with each contribution (https://coveralls.io/github/cuthbertLab/music21). CI measures it on one pinned Python, a middle supported version, so failures on the newest and oldest return first. # pragma: no cover exists for genuinely untriggerable code and is otherwise discouraged.