Run your first scenario

Install

Use Python 3.10 or later and install niltest into the virtual environment that will run it. Command names differ by operating system and Python installation.

Windows commonly uses python -m pip, while Ubuntu and macOS commonly use python3 -m pip. After activation, a virtual environment usually exposes its interpreter as python and its installer as pip on every OS.

pip install and pip3 install may also work. Using python -m pip or python3 -m pip is safer because it explicitly selects the Python receiving the package.

Declare a case

given contains real keyword arguments and returns describes the expected result. Use names that explain the behavior to another developer.

import niltest
from niltest import Mode, expect, scenario

niltest.configure(mode=Mode.TEST)  # @scenarioより前

@scenario("配送料")
def shipping_fee(subtotal: int, premium: bool = False) -> int:
    if expect:
        expect.case(
            "プレミアム会員は無料",
            given={"subtotal": 1_000, "premium": True},
            returns=0,
        )

    return 0 if premium or subtotal >= 5_000 else 500

Run from the CLI

Pass the import path of the module that defines your scenarios. A successful run exits with code 0.

niltest run your_package.specs --language ja

Where to go next

• Return fixed values while developing → Mocking
• Check types or dynamic conditions → Expectations
• Add niltest to CI → Running checks