pytest run only the changed file?

Question

I'm fairly new to Python, trying to learn the toolsets.

I've figured out how to get py.test -f to watch my tests as I code. One thing I haven't been able to figure out is if there's a way to do a smarter watcher, that works like Ruby's Guard library.

Using guard + minitest the behavior I get is if I save a file like my_class.rb then my_class_test.rb is executed, and if I hit enter in the cli it runs all tests.

With pytest so far I haven't been able to figure out a way to only run the test file corresponding to the last touched file, thus avoiding the wait for the entire test suite to run until I've got the current file passing.

How would you pythonistas go about that?

Thanks!

score 43 · Accepted Answer · answered Jan 30 '16 at 12:36

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One possibility is using pytest-testmon together with pytest-watch.

It uses coverage.py to track which test touches which lines of code, and as soon as you change a line of code, it re-runs all tests which execute that line in some way.

answered Jan 30 '16 at 12:36

The Compiler

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That's working pretty well for me. Thanks very much for the suggestion! – Andrew Feb 01 '16 at 00:37
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in coveragepy 5.0 this would be native ( [see this post](https://nedbatchelder.com/blog/201810/who_tests_what_is_here.html)) – Sik Nov 28 '18 at 17:32
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can you elaborate on how you combine these? – endolith Sep 02 '19 at 14:52
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@endolith See the last line of the "Usage" section of https://pypi.org/project/pytest-testmon/ – The Compiler Sep 07 '19 at 17:26
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Can you elaborate in your answer? Depending on links to other sites is discouraged because of link rot, etc – endolith Sep 08 '19 at 18:25
Which has actually happened in this case – Craig Brett Oct 01 '19 at 12:53

Ben R · Answer 2 · 2021-03-10T11:39:31.390

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To add to @The Compiler's answer above, you can get pytest-testmon and pytest-watch to play together by using pytest-watch's --runner option:

ptw --runner "pytest --testmon"

Or simply:

ptw -- --testmon

edited Mar 10 '21 at 11:39

answered Nov 02 '19 at 01:03

Ben R

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it seems a bit slow... Is there any way to speed it up? – Norfeldt Jul 29 '20 at 07:48

score 8 · Answer 3 · answered Feb 27 '18 at 08:45

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There is also pytest-xdist which has a feature called:

--looponfail: run your tests repeatedly in a subprocess. After each run py.test waits until a file in your project changes and then re-runs the previously failing tests. This is repeated until all tests pass after which again a full run is performed.

answered Feb 27 '18 at 08:45

einSelbst

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This solution is the best of this SO thread. It is simpler than testmon+watch and it worked with async tests (with pytest-trio) where the other solution failed. – Mathieu CAROFF Apr 15 '20 at 16:48
as of pytest-xdist 3.0.2, the `-looponfail` argument has been deprecated. – Harshil Mehta Jan 12 '23 at 13:18

score 8 · Answer 4 · answered Jul 29 '20 at 07:53

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The fastest setup I got was when I combines @lmiguelvargasf @BenR and @TheCompiler answer into this

ptw --runner "pytest --picked --testmon"

you first gotta have them installed by

pip3 install pytest-picked pytest-testmon pytest-watch

answered Jul 29 '20 at 07:53

Norfeldt

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score 6 · Answer 5 · answered Jul 07 '20 at 22:56

If you are using git as version control, you could consider using pytest-picked. This is a plugin that according to the docs:

Run the tests related to the unstaged files or the current branch

Demo

Basic features

Run only tests from modified test files
Run tests from modified test files first, followed by all unmodified tests

Usage

pytest --picked

pytest run only the changed file?

5 Answers5

Basic features

Usage