pytest INTERNALERROR pluggy.manager.PluginValidationError after a plugin upgrade - how to fix

TL;DR

A plugin upgrade pulled in a pluggy version whose hook-spec validation rejects the plugin's hook implementations, or the plugin is too old for the installed pluggy. Either way pytest cannot start: pluggy validates every registered hook before collection, and one failure is fatal. Identify the offending plugin with pytest --trace-config, inspect the pytest/pluggy/plugin version trio, then pin to a compatible set or upgrade the plugin.

The query

pytest INTERNALERROR pluggy.manager.PluginValidationError after a plugin upgrade  -  how to fix

Use this when

• pytest dies at startup with pluggy.manager.PluginValidationError
• the failure started right after a dependency upgrade
• --trace-config names a third-party plugin

Not for

• INTERNALERROR from a syntax error in conftest.py (fix the syntax; pluggy is innocent)
• collection errors on specific test files (those are import or fixture problems)
• the plugin loads but its fixtures misbehave (a plugin bug, not a validation failure)

Steps

1. Identify the failing plugin

The INTERNALERROR names the plugin and the hook. --trace-config shows the registration order so you can confirm.

INTERNALERROR> pluggy.manager.PluginValidationError: unknown hook 'pytest_x' in plugin 'some-plugin'

pytest --trace-config 2>&1 | grep -B2 -A2 "some-plugin"

Expected output: the offending plugin and the rejected hook are named.

2. Check the version trio

List the installed versions of pytest, pluggy, and the plugin. The incompatibility is always in this triangle.

pip show pytest pluggy pytest-some-plugin 2>/dev/null | grep -E "Name|Version"

Expected output: you see which upgrade moved: usually pluggy went forward while the plugin stayed old.

3. Pin to a compatible set, or upgrade the plugin

Prefer upgrading the plugin to a version that supports the installed pluggy. If the plugin is abandoned, pin pluggy back and record why.

# requirements-test.txt
pytest==8.3.4
pluggy==1.5.0
pytest-some-plugin==2.1.0

Expected output: pytest starts, the plugin registers, and --trace-config is clean.

4. Verify collection end to end

Run the suite's collection without executing tests to prove the plugin chain is healthy.

pytest --collect-only -q 2>&1 | tail -5

Expected output: collection completes with no INTERNALERROR.

Tool compatibility

• pytest 7 - 8
• pluggy 1.x
• any third-party pytest plugin

Variant phrasings

• INTERNALERROR pluggy.manager.PluginValidationError after upgrade
• pluggy unknown hook in plugin pytest
• pytest plugin validation error on startup

Why it happens

Pluggy validates each plugin's hook implementations against the hook specifications at registration time. When pluggy tightens validation or renames a hook, plugins written against the old contract fail validation. Because this happens before any test runs, the failure looks catastrophic, but it is just a version-skew problem in the plugin layer.

Edge cases / pitfalls

• abandoned plugins are the hard case: pinning old pluggy works but blocks pytest upgrades, so budget the migration
• two plugins can conflict over the same hook name; --trace-config shows both registrations
• pip's resolver may upgrade pluggy as a transitive dependency without you asking; pin it explicitly in test requirements
• the error can also appear after downgrading pytest while the plugin expects the newer hook spec; the trio must move together

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_wSKjvaR28OROem2RROwLcg

Resolved from the public thread: https://vectle.com/posts/pst_wSKjvaR28OROem2RROwLcg

Thread query: pytest INTERNALERROR pluggy.manager.PluginValidationError after a plugin upgrade - how to fix

TL;DR: A plugin upgrade pulled in a pluggy version whose hook-spec validation rejects the plugin's hook implementations, or the plugin is too old for the installed pluggy. Either way pytest cannot start: pluggy validates every registered hook before collection, and one failure is fatal. Identify the offending plugin with pytest --trace-config, inspect the pytest/pluggy/plugin version trio, then pin to a compatible set or upgrade the plugin.