Unit tests in Nix

Create a file, name it test.bats:

#!/usr/bin/env bats

@test "addition using bc" {
  result="$(echo 2+2 | bc)"
  [ "$result" -eq 4 ]
}

@test "addition using dc" {
  result="$(echo 2 2+p | dc)"
  [ "$result" -eq 4 ]
}

@test "Ant is installed" {
  ant -version
}

Make it executable: chmod +x test.bats.

Run the test in nix-shell:

$ nix-shell -p bats -p ant --run ./test.bats
 ✓ addition using bc
 ✓ addition using dc
 ✓ Ant is installed

3 tests, 0 failures

At least for availability of packages, you can now test this way!

And if bats itself is not available ‒ well, then you will also get an error from your tests ‒ which is very good!

If at some time you want to parallelize your test execution, add a -j [N_JOBS] parameter to the call (requires GNU Parallel).

For example, on a machine with 8 CPU cores, that could become:

$ nix-shell -p bats -p ant --run "./test.bats -j 8"