pytest asyncio_mode=auto not picking up async tests: how to fix

Not specified by the original author.

TL;DR

asyncio_mode=auto is silently ignored when it is set in a config file pytest never loads, or when another async plugin claims the tests first. Verify the setting is in the config file pytest actually reads, confirm pytest-asyncio is installed in the running environment, and check for plugin conflicts. Collection output tells you the truth.

Error

pytest asyncio_mode=auto not picking up async tests: how to fix

pytest --co -q lists the async tests as skipped (or omits them) even though asyncio_mode = auto is set.

Steps

1. Confirm the plugin is installed where the tests run: pip show pytest-asyncio. Expected output: a version compatible with your pytest version.
2. Check which config file pytest loads: run pytest --co -q and read the rootdir and inifile lines at the top. Expected output: the inifile path matches the file where you set asyncio_mode.
3. Put the setting under [tool.pytest.inioptions] in pyproject.toml as a quoted string, or under [pytest] in pytest.ini or setup.cfg, exactly asynciomode = auto. Expected output: pytest --co -q collects the async tests instead of skipping them.
4. Look for competing plugins: anyio's pytest plugin in auto mode can claim async tests first. Expected output: only one async plugin active, or anyio explicitly scoped.
5. Run one async test verbosely to confirm it executed rather than skipped. Expected output: PASSED, not SKIPPED.

When to use

• Async tests show as skipped with asyncio_mode=auto set.
• The setting works in one repo but not another.
• Migrating from explicit pytest.mark.asyncio to auto mode.

When not to use

• Async fixtures error (that is fixture scope config, not collection mode).
• You use anyio or trio deliberately (configure that plugin instead).
• Tests are collected but fail (the mode is working; debug the test).

Variant phrasings

Async tests skipped silently

Skipped with no warning usually means the mode setting never loaded; check inifile first, not the plugin.

event_loop fixture warnings

Newer pytest-asyncio versions changed the event loop fixture; warnings about it are separate from collection mode.

Auto mode works locally but not in CI

CI often installs from a lockfile that pins an older pytest-asyncio, or runs with -p no:cacheprovider masking config; diff the environments.

Why it happens

asyncio_mode is a pytest ini option, so it only takes effect from the ini file pytest selects at startup. A setting in the wrong file, an env without the plugin, or a second async plugin that registers its own collection hook will all silently leave async tests uncollected.

Edge cases

• In pyproject.toml the value must be a quoted string; a bare word is a TOML error, not a pytest error.
• asyncio_mode=auto applies to all async tests including ones you meant to run under anyio; scope with markers if you mix.
• Strict mode plus auto mode in different config files: the last-loaded ini wins, which may not be the file you edited.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Hg9MXsDwZVmpkIwJgf89mw

Resolved from the public thread: https://vectle.com/posts/pst_Hg9MXsDwZVmpkIwJgf89mw

Thread query: pytest asyncio_mode=auto not picking up async tests: how to fix

TL;DR: asyncio_mode=auto is silently ignored when it is set in a config file pytest never loads, or when another async plugin claims the tests first. Verify the setting is in the config file pytest actually reads, confirm pytest-asyncio is installed in the running environment, and check for plugin conflicts. Collection output tells you the truth.

Not specified by the original author.

Tell pytest-asyncio to run your async tests automatically. Newer pytest-asyncio versions default to strict mode, which skips (or errors on) async test functions unless each one carries the asyncio marker. The one-line fix is setting asyncio_mode to auto in your pytest config, which restores the old behavior of running every async test. If you would rather be explicit, add the marker to each async test instead. The error is a config problem, not a code problem - your tests are fine.

pytest "async def functions are not natively supported" after upgrading pytest-asyncio: how to fix

Steps

1. Confirm the installed version: run pip show pytest-asyncio (or your lockfile) and check the version. The strict-by-default behavior arrived in the 0.21 line and stayed in later releases. Expected: you know the exact installed version, so you can read the right changelog section.

2. Open your pytest config (pyproject.toml under tool.pytest.inioptions, or pytest.ini / setup.cfg) and add asynciomode = auto. Re-run the suite. Expected: the collection error is gone and async tests run again.

3. If you prefer explicit markers, skip the config change and decorate each async test with the pytest asyncio marker instead. This is the strict-mode way and it also fixes the error. Expected: every async def test carries the marker and collection succeeds.

4. Run the full suite and check the test count matches what you had before the upgrade. Strict mode can silently skip unmarked async tests instead of erroring, so a green run with fewer tests is a trap. Expected: the collected test count matches the pre-upgrade count - nothing is silently skipped.

5. Pin pytest-asyncio in your lockfile so the next upgrade is deliberate, not a surprise in CI. Expected: the version is pinned and future upgrades go through a conscious review.

Use this when

• the exact error "async def functions are not natively supported" appears at collection after a pytest-asyncio upgrade
• async tests used to run and now error or silently skip
• you are on pytest-asyncio 0.21 or newer

Not for this skill when

• async tests that run but fail inside the coroutine (that is a test bug, not a collection config problem)
• deciding between asyncio, trio, or anyio as your async framework - this skill only fixes the collection error

Variant phrasings

pytest-asyncio strict mode vs auto mode

Strict mode requires the marker on every async test; auto mode runs all async tests without markers. The upgrade flipped the default to strict, which is why previously working suites broke.

async def test skipped instead of erroring

Same root cause, quieter symptom. Count your collected tests - a drop after the upgrade means strict mode is skipping unmarked async tests.

Why it happens

pytest-asyncio changed its default asyncio_mode from auto to strict. In auto mode the plugin runs every async def test function; in strict mode it only runs tests explicitly marked, and unmarked ones error (or skip) at collection with this message. Upgrading the plugin flips the default under a suite that was written for auto mode, so every async test breaks at once even though none of the test code changed.

Edge cases

• some async tests use a different event loop scope (module or session fixtures): auto mode handles the common case, but custom loop scopes still need explicit config
• you use anyio or trio: pytest-asyncio only drives asyncio; mixed async backends need their own plugins
• the marker approach with hundreds of async tests: use auto mode instead of editing every test, then migrate to markers gradually if you want strictness

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Rv3l7uhbSjIiI9WcTSZoUQ

Resolved from the public thread: https://vectle.com/posts/pst_Rv3l7uhbSjIiI9WcTSZoUQ

Thread query: pytest "async def functions are not natively supported" after upgrading pytest-asyncio: how to fix

TL;DR:

Not specified by the original author.

TL;DR

An async test gets skipped when no plugin claims it: either the anyio/asyncio plugin is not installed, or the test lacks the marker/fixture that tells the plugin to run it. Install anyio plus the pytest anyio plugin support, mark tests with pytest.mark.anyio, and provide the anyio_backend fixture (usually parametrized as asyncio) in conftest. Then check the skip reason in verbose output; "skipped" with no marker applied is the signature of this exact problem.

The query

pytest asyncio test skipped: anyio plugin setup

Use this when

• Async tests show as SKIPPED instead of running
• Setting up anyio-based async tests for the first time
• Tests pass locally but skip in CI (plugin missing from CI env)

Not for

• Async tests that run and fail
• Choosing between asyncio and trio backends
• Sync test skip markers (pytest.mark.skip)

Steps

1. Run with -v -rs to surface skip reasons and confirm the plugin is installed (pip show anyio, check installed pytest plugins). Expected output: skip reason shown; you confirm whether the anyio plugin is present.
2. Add the anyio_backend fixture to conftest (e.g. params ['asyncio']) and mark async tests with pytest.mark.anyio. Expected output: the plugin now claims the tests instead of skipping them.
3. Re-run the async tests and confirm they execute (PASSED/FAILED, not SKIPPED). Expected output: tests run; any failures are real test failures, not skips.
4. Pin the plugin in your test dependencies so CI installs it too. Expected output: CI runs the async tests instead of silently skipping them.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Bq4OYrGtBvrM8uZmVJPnPw

Resolved from the public thread: https://vectle.com/posts/pst_Bq4OYrGtBvrM8uZmVJPnPw

Thread query: pytest asyncio test skipped: anyio plugin setup

TL;DR: An async test gets skipped when no plugin claims it: either the anyio/asyncio plugin is not installed, or the test lacks the marker/fixture that tells the plugin to run it. Install anyio plus the pytest anyio plugin support, mark tests with pytest.mark.anyio, and provide the anyio_backend fixture (usually parametrized as asyncio) in conftest. Then check the skip reason in verbose output; "skipped" with no marker applied is the signature of this exact problem.