Hey there! I’m writing unit tests using Pytest and the metaflow.Runner class. Here is what a simple test looks like:

from metaflow import Run, Runner

def test_sample():
    metaflow_data = run_pipeline()
    assert metaflow_data.mlflow_run_id is not None


def run_pipeline():
    with Runner("pipelines/training.py", environment="conda").run() as running:
        return Run(running.run.pathspec).data

This works for some of the flows, but it fails for the

training.py

flow in this example because that file imports some functions from a separate

common.py

file. Here is the directory structure:

├── pipelines/
│   ├── training.py
│   └── common.py
└── tests/
    └── test_sample.py

Here is the error I get when I try to run the test (and the

Runner

tries to execute the training flow):

>   from common import packages
E   ModuleNotFoundError: No module named 'common'

I tried fixing this problem by adding a symlink inside

/tests

pointing to

/pipelines

. I also tried to fix it by passing

cwd

to

Runner

pointing to the

/pipelines

folder. Any suggestions?

There is a cwd arg in the Runner constructor, which I think is supposed to work like

Runner(..., cwd="../pipelines")

. @brainy-truck-72938 could you confirm?

The

cwd

argument is there, but I can’t get it to work. I’ve tried this: 1. Setting

cwd

to the relative location of `/pipelines`:

cwd="../pipelines"

2. Setting it to the absolute path:

cwd="/Users/…/pipelines/"

It doesn’t work in either case.

hmm maybe I misinterpreted the docs. Another option is to symlink from

tests/common.py

to point at the actual

pipelines/common.py

file. On the SDK-based path, I'll wait for Madhur or someone with more knowledge of that feature to answer.

Let’s wait for an SDK-related answer. The symlinks don’t work either when using the Runner class. (Symlinks do work when running flows using

subprocess

as specified here: https://docs.outerbounds.com/use-pytest/)

Hi @glamorous-pillow-95848 currently, the

cwd

argument only affects where the

subprocess

execution will take place, it doesn't affect where the flow file is loaded from. Thus, the

cwd

option doesn't work, because at the time of loading the file, the

from common import packages

needs to work.. I was able to make it work by using

PYTHONPATH

i.e.

PYTHONPATH=/Users/madhur/Desktop/outerbounds/office-hours/sant/pipelines python tests/test_sample.py

here, the folder

sant

has this structure:

. <-- this is `sant`
├── pipelines
│   ├── common.py
│   └── training.py
└── tests
    └── test_sample.py

Okay, so the

PYTHONPATH

workaround works… but it’s ugly 🙂 It looks like you submitted a patch to fix this without having to use

PYTHONPATH

or

cwd

. Is that what the patch does?

yeah, it does:

flow_dir = os.path.dirname(os.path.abspath(flow_file))
sys.path.insert(0, flow_dir)

and then also removes it later in a

finally

block

sys.path.remove(flow_dir)

Awesome! You rock! I’ll wait for the patch to make it into the library. I have everything working now with

PYTHONPATH

(set via pytest.ini), but it breaks Metaflow’s colors and it feels like a hack.

yeah, I will post a note about this PR internally to accelerate

Good to know. Thanks!