Most likely, this is a dependency compatibility issue, not a problem with your test code. Cause

prefect_test_harness

exercises Prefect async internals, and your environment is probably using a newer

anyio

version where

TaskGroup

gained a new required abstract method:

create_task

. Prefect has an internal class called

GatherTaskGroup

that subclasses

anyio.abc.TaskGroup

. If that Prefect version does not implement the new

create_task

method, Python raises:

text
TypeError: Can't instantiate abstract class GatherTaskGroup with abstract method create_task

So the usual reason is: Your installed Prefect version is incompatible with your installed

anyio

version. What to check Run:

bash
pip show prefect anyio

If you see a very recent

anyio

version, that’s the likely trigger. Typical fix Try pinning

anyio

to an earlier compatible version, for example:

bash
pip install "anyio<4.14.0"

or add a constraint in your project config. You can also try upgrading Prefect to the latest release in case a fix has already landed:

bash
pip install -U prefect

Recommended order 1. Upgrade Prefect 2. If it still fails, pin

anyio<4.14.0

Why it shows up in tests

prefect_test_harness

spins up Prefect testing infrastructure and touches async orchestration code paths that instantiate this task group, so the incompatibility often appears there first. Helpful links - Prefect docs: Prefect documentation - Prefect releases: Prefect release notes If you want, I can help you figure out the exact compatible version pair for your current Prefect install.