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Select a portion of the collected tests

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Select a portion of the collected tests, so you can run diferents parts of your test suite in differents instances to balance the number of test run on each one.

Use case

Suppose you have a big, slow test suite, but you can trigger several CI workers to run different portions of it, in a sake lazy/simple way to parallelize it.

A basic, obvious way to do that is to explictily collect from different directories/modules

  • worker1: pytest tests/a (100 tests, ~4 minutes to finish)
  • worker2: pytest tests/b (20 tests, ~1 minute to finish)
  • worker3: pytest tests/c tests/d (30 tests, ~1 minute to finish)

The problem is that directory tests/a may have a lot more tests that tests/c plus test/d, so worker1 takes a lot more to finish.

With pytest-portion you can still split the tests in different instances, but letting the extension makes the selection in a more balanced way.

  • worker1: pytest --portion 1/3 tests (first 50 tests, ~2 minutes)
  • worker2: pytest --portion 2/3 tests (next 50 tests, ~2 minutes)
  • worker3: pytest --portion 3/3 tests (last 50 tests, ~2 minutes)

In this case, the tests of all the directories are collected, but only a third (a different one!) of them will be actually executed on each worker.

Note this balance is by number of tests, so if there is very slow tests in a particular portion, the duration may not be expected.

For a fine tuning, you could pass the portion in a more explicit way:

  • worker1: pytest --portion 0:0.5 tests (first half, 1st to 75th test)
  • worker2: pytest --portion 0.5:0.8 tests (next 30%, from 76th to 125º)
  • worker3: pytest --portion 0.8:1 tests (last 20%)


You can install “pytest-portion” via pip from PyPI:

$ pip install pytest-portion


Pass --portion <i/n> where:

  • n is the number of portions
  • i is the i-th portion to select (1 <= i <= n)


If the number of tests collected is not divisible by n, the last portion will contain the rest. For instance, if you have test_1, test_2 and test_3, –portion 1/2 will run the first one, and –portion 2/2 the last 2.

Alternatively --portion start:end where:

  • start and end are the coefficient (between 0 and 1) that represent the segment of the collected tests to select.


Contributions are very welcome. Please ensure the coverage at least stays the same before you submit a pull request.


Distributed under the terms of the BSD-3 license, “pytest-portion” is free and open source software


If you encounter any problems, please file an issue along with a detailed description.


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