This rule raises an issue when a test parameterization mechanism is configured with an empty collection as the source of test values.

In Python with pytest, this specifically occurs when using the @pytest.mark.parametrize decorator with an empty sequence (list, tuple, or other iterable) as the values argument.

Why is this an issue?

Passing an empty list to @pytest.mark.parametrize collects the test but skips it with got empty parameter set for (…​). The suite still passes while providing no coverage for that function.

When @pytest.mark.parametrize has no value sets to iterate over, the test is silently skipped during collection:

• Your test suite appears to pass, but this test isn’t actually running
• You have no test coverage for the function being tested
• Bugs in your code may go undetected

This situation typically occurs due to:

• Accidentally deleting or commenting out all test cases
• Incomplete test implementation (test structure created but cases not yet added)
• Copy-paste errors when creating new tests
• Refactoring mistakes where test cases were moved or removed

Unlike mistakes that cause failures, an empty parametrized test collection fails silently. The test won’t raise an error — it simply won’t run, which makes the problem easy to miss until you discover missing coverage.

An empty parameter list is never a valid end state for a committed test. Suppressing this issue is not appropriate, as the test will not run until values are provided.

What is the potential impact?

Regressions can go undetected when tests are skipped silently without failing the build.

How to fix it

Add at least one case tuple to the @pytest.mark.parametrize values list so the test body actually runs.

If the test is not ready yet, do not simply remove the decorator while keeping its parameters: pytest will treat those names as fixtures and fail at setup with fixture '…​' not found. Instead, either add the missing cases, rewrite the test without parametrization (inline the values in the function body), or mark the test explicitly with @pytest.mark.skip(reason="…​") on a parameterless function.

Code examples

Noncompliant code example

import pytest

@pytest.mark.parametrize('operand,expected', [])
def test_double(operand, expected):
    assert double(operand) == expected  # Noncompliant

Compliant solution

import pytest

@pytest.mark.parametrize('operand,expected', [
    (1, 2),
    (2, 4),
    (3, 6),
    (0, 0),
])
def test_double(operand, expected):
    assert double(operand) == expected

Resources

Documentation

• pytest documentation - How to parametrize fixtures and test functions
• pytest documentation - pytest.mark.parametrize