I wrote two days ago about how our pytest suite was slow, and how we could speed it up by blessing a suite-wide fixture that was scoped to session. This was true! But, like a one-year-old with a hammer, I found myself so gratified by the act of swinging that I found myself also trying to pinpoint another performance issue: why does it take so long to run a single smoke test?

There are a lot of known problems: for instance, import stripe takes 400ms. But there was an eight second lag between starting pytest and the first test running, and I wanted to know why.

All I needed to do was run pyinstrument -m pytest -k test_smoke and I got three useful results that I am cataloging in hopes they might find you:

1. boto3 hits AWS upon client instantiation, and we had a dependencies file that imported and created the client. Easy fix: just lazily instantiate it.
2. We were globbing actions/*.py to run a test on every single one of our "actions" (see Use weird tests to capture tacit knowledge). Turns out: this took 2 seconds. Another fix, though less easy: move the globbing output to an autogen file and read from that instead. (Causes a bit of a Rube Goldberg effect, but it's worth it.)
3. Two more heavy imports (each at 500ms): one for parsing msg files, the other for parsing iCal. Unlike Stripe, the surface area here is fairly well-contained, so it was easy to move things around to lazily import them.