nixpkgs/doc/builders/testers.chapter.md

Testers

This chapter describes several testing builders which are available in the testers namespace.

testVersion

Checks the command output contains the specified version

Although simplistic, this test assures that the main program can run. While there's no substitute for a real test case, it does catch dynamic linking errors and such. It also provides some protection against accidentally building the wrong version, for example when using an 'old' hash in a fixed-output derivation.

Examples:

passthru.tests.version = testVersion { package = hello; };

passthru.tests.version = testVersion {
  package = seaweedfs;
  command = "weed version";
};

passthru.tests.version = testVersion {
  package = key;
  command = "KeY --help";
  # Wrong '2.5' version in the code. Drop on next version.
  version = "2.5";
};

testEqualDerivation

Checks that two packages produce the exact same build instructions.

This can be used to make sure that a certain difference of configuration, such as the presence of an overlay does not cause a cache miss.

When the derivations are equal, the return value is an empty file. Otherwise, the build log explains the difference via nix-diff.

Example:

testEqualDerivation
  "The hello package must stay the same when enabling checks."
  hello
  (hello.overrideAttrs(o: { doCheck = true; }))

invalidateFetcherByDrvHash

Use the derivation hash to invalidate the output via name, for testing.

Type: (a@{ name, ... } -> Derivation) -> a -> Derivation

Normally, fixed output derivations can and should be cached by their output hash only, but for testing we want to re-fetch everytime the fetcher changes.

Changes to the fetcher become apparent in the drvPath, which is a hash of how to fetch, rather than a fixed store path. By inserting this hash into the name, we can make sure to re-run the fetcher every time the fetcher changes.

This relies on the assumption that Nix isn't clever enough to reuse its database of local store contents to optimize fetching.

You might notice that the "salted" name derives from the normal invocation, not the final derivation. invalidateFetcherByDrvHash has to invoke the fetcher function twice: once to get a derivation hash, and again to produce the final fixed output derivation.

Example:

tests.fetchgit = invalidateFetcherByDrvHash fetchgit {
  name = "nix-source";
  url = "https://github.com/NixOS/nix";
  rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
  sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
};