parametrize in Python

One test body, a row of cases, and a separate result for each.

import pytest


def wpm(chars, seconds):
    return (chars / 5) / (seconds / 60)


@pytest.mark.parametrize("chars,seconds,expected", [
    (400, 60, 80.0),
    (200, 60, 40.0),
    (400, 30, 160.0),
])
def test_wpm(chars, seconds, expected):
    assert wpm(chars, seconds) == pytest.approx(expected)


@pytest.mark.parametrize("chars", [0, 100])
@pytest.mark.parametrize("seconds", [30, 60])
def test_never_negative(chars, seconds):
    assert wpm(chars, seconds) >= 0

How it works

1. The ids in the report come from the parameters.
2. Several parameters multiply into a grid.
3. It replaces a loop inside a single test, which hides failures.

Keywords and builtins used here

• assert
• def
• return
• test_never_negative
• test_wpm
• wpm

The run, in numbers

Lines

20

Characters to type

445

Tokens

133

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 80 seconds.

Type this snippet

Step 3 of 3 in Writing tests, step 3 of 9 in Testing with pytest.

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