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Test Script Linting

The NixOS test driver can validate your Python testScript before the test is executed. This catches common mistakes early, before resources are wasted on failures that could have been detected at build time.

Benefits

  • Early Error Detection

    Catch obvious syntax mistakes and logic errors before starting long-running VMs or containers.

  • Increased CI efficiency

    Prevent trivially broken test scripts from wasting CI time and resources.

How it Works

The testScript is Python code embedded in your test definition. When the test is built, the driver runs:

  • Pyflakes to lint the script and catch common Python mistakes
  • mypy to type-check the script

This means syntax issues, undefined names, and many type-related mistakes are reported before the test itself starts running.

Skipping Checks During Development

For rapid local iteration, the test options reference in the NixOS manual provides two escape hatches:

test.nix
{
  name = "my test";

  skipLint = true;      # disables the Pyflakes check
  skipTypeCheck = true; # disables the mypy check

  # ...
}

Both options default to false.

Disabling these checks can speed up rebuilds while you are changing a test frequently. That can be useful during development, but tests with linting or type-checking disabled should generally not be committed to production repositories.