Unit tests for nix functions

jlesquembre · December 2, 2020, 10:04pm

How are you testing your nix functions? I’m writing some helper nix functions and I’d like to add some tests, but I didn’t find much about testing nix functions.

I found this project: GitHub - nix-community/nixt: Simple unit-testing for Nix [maintainer=@Lord-Valen]
It looks promising, but I don’t understand how to write a test with it

bjornfor · December 4, 2020, 10:58pm

There is a runTests function in nixpkgs/lib/debug.nix. It seems many (all?) nixpkgs/lib/tests are using that.

jlesquembre · December 7, 2020, 9:57am

thanks @bjornfor, I need to get my head around about how to run them. But the docs:

github.com

NixOS/nixpkgs/blob/6571462647d7316aff8b8597ecdf5922547bf365/lib/debug.nix#L154-L166


      
          /* Evaluate a set of tests.  A test is an attribute set `{expr,
             expected}`, denoting an expression and its expected result.  The
             result is a list of failed tests, each represented as `{name,
             expected, actual}`, denoting the attribute name of the failing
             test and its expected and actual results.
          
          
   Used for regression testing of the functions in lib; see
             tests.nix for an example. Only tests having names starting with
             "test" are run.
          
          
   Add attr { tests = ["testName"]; } to run these tests only.
          */
          runTests =

and this example:

github.com

NixOS/nixpkgs/blob/003b68aead6ecd67e9ab47c81ab2f6aae06bcf97/pkgs/test/kernel.nix#L47-L51


      
          runTests {
            testEasy = {
              expr = (getConfig { NIXOS_FAKE_USB_DEBUG = yes;}).NIXOS_FAKE_USB_DEBUG;
              expected = { tristate = "y"; optional = false; freeform = null; };
            };

are a good starting point