unit testing - Is there a Javascript equivalent to pytest's parameterized fixtures? - Stack Overflow

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In pytest you can set up fixtures that can have multiple different values. These are called "parameterized fixtures". A test that uses these fixtures will be run with all possible binations of values from those fixtures.

Example

# Fixture `a` can have the values `1` and `2`
@pytest.fixture(params=[1, 2])
def a(request):
    yield request.param

# Fixture `b` can have the values `3` and `4`
@pytest.fixture(params=[3, 4])
def b(request):
    yield request.param

# The test `test_sum` uses the fixtures `a` and `b`
def test_sum(a, b):
    assert sum([a, b]) == a + b

Here, the function test_sum will be run four times in total. Each run will use different arguments: a=1, b=3, a=1, b=4, a=2, b=3, and a=2, b=4 respectively.

Question

Is there an equivalent to parametrized fixtures in any Javascript testing library? (We currently use mocha, so that would be the most interesting to us)

In pytest you can set up fixtures that can have multiple different values. These are called "parameterized fixtures". A test that uses these fixtures will be run with all possible binations of values from those fixtures.

Example

# Fixture `a` can have the values `1` and `2`
@pytest.fixture(params=[1, 2])
def a(request):
    yield request.param

# Fixture `b` can have the values `3` and `4`
@pytest.fixture(params=[3, 4])
def b(request):
    yield request.param

# The test `test_sum` uses the fixtures `a` and `b`
def test_sum(a, b):
    assert sum([a, b]) == a + b

Here, the function test_sum will be run four times in total. Each run will use different arguments: a=1, b=3, a=1, b=4, a=2, b=3, and a=2, b=4 respectively.

Question

Is there an equivalent to parametrized fixtures in any Javascript testing library? (We currently use mocha, so that would be the most interesting to us)

• javascript
• unit-testing
• mocha.js
• pytest

Share Improve this question Follow edited Dec 7, 2017 at 10:19 qff asked Dec 7, 2017 at 10:04 qffqff 5,96233 gold badges4343 silver badges6565 bronze badges 1

• 2 I'm looking for the same stuff. Surprisely, pytest's fixture alike feature has been requested for years. However, these JS testing frontiers never really understand how elegant the tests can be when with builtin fixture. – Tim Wu Commented Mar 23, 2018 at 23:34

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3 Answers 3

Sorted by: Reset to default 4

Jest now incorporated the utility into its codebase :) It's under it.each/test.each. For older versions of jest, you can use one of the libraries mentioned below.

Old answer:

Recently, I discovered there is a utility for Jest called jest-each or with less nice syntax jest-in-case which is quite a good alternative to pytest.mark.parametrized.

Old old original answer below:

Unfortunately no. Mocha does not support it even today from what I found on the internet. There is also rejected proposal(s) for such syntax, but currently, the only solution is something that they call dynamically generating tests and the syntax looks like in the code below (taken from the doc). Also, you can read more about sad state of JS vs. Python testing.

describe('Possible user names behaves correctly ', () => {
  const TEST_CASES = [
    {args: ['rj'], expected: false},
    {args: ['rj12345'], expected: false},
    {args: ['rj123'], expected: true},
  ]

  TEST_CASES.forEach((testCase) => {
    it(`check user name ${JSON.stringify(testCase.args)}`, () => {
      const result = checkUserName.apply(this, testCase.args)

      expect(testCase.expected).toEqual(result)
    })
  })
})

Having encountered the need for parameterized tests for both python and js, I think the one that is both easy to use and readable is the .each syntax included in Jest (sorry, haven't found options for Mocha!).

A good example can be found here: https://dev.to/flyingdot/data-driven-unit-tests-with-jest-26bh

Playwright Test testing framework borrows this concept from PyTest; see https://playwright.dev/docs/test-fixtures for details.

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