Switch to bats over pytest

This removes python entirely from the stack.
Yet to run the tests on macOS, but they're buildable by way of nix
wrapping. Worst case scenario, you cannot run them from the devshell
but `nix run .#test-runner-<latest||stable>` should work okay.

Author: bbenne10

.envrc

@@ -1,5 +1,9 @@
 # shellcheck shell=bash
 strict_env
 source ./direnvrc
-watch_file direnvrc ./*.nix
+
+watch_file direnvrc
+# shellcheck disable=SC2046
+watch_file $(find . -name "*.nix")
+
 use flake

flake.nix

@@ -33,25 +33,18 @@
             self',
             ...
           }:
+          let
+            nix-direnv = pkgs.callPackage ./default.nix { };
+            test_pkgs = pkgs.lib.callPackagesWith pkgs ./tests { inherit nix-direnv; };
+          in
           {
-            packages = rec {
-              nix-direnv = pkgs.callPackage ./default.nix { };
-              default = config.packages.nix-direnv;
-              test-runner-stable = pkgs.callPackage ./test-runner.nix {
-                nixVersion = "stable";
-                inherit nix-direnv;
-              };
-              test-runner-latest = pkgs.callPackage ./test-runner.nix {
-                nixVersion = "latest";
-                inherit nix-direnv;
-              };
+            packages = test_pkgs // {
+              inherit nix-direnv;
+              default = nix-direnv;
             };
 
             devShells.default = pkgs.callPackage ./shell.nix {
-              packages = [
-                config.treefmt.build.wrapper
-                pkgs.shellcheck
-              ];
+              treefmt = config.treefmt.build.wrapper;
             };
 
             checks =

shell.nix

@@ -1,14 +1,27 @@
 {
   pkgs ? import <nixpkgs> { },
-  packages ? [ ],
+  treefmt ? null,
+  nix-direnv ? (pkgs.callPackage ./default.nix { }),
+  test_pkgs ? (pkgs.lib.callPackagesWith pkgs ./tests { inherit nix-direnv; }),
 }:
-
-with pkgs;
-mkShell {
-  packages = packages ++ [
-    python3.pkgs.pytest
-    python3.pkgs.mypy
-    ruff
-    direnv
+let
+  inherit (pkgs) lib;
+in
+pkgs.mkShell {
+  DIRENV_STDLIB = "${test_pkgs.direnv-stdlib}";
+  DIRENVRC = "${nix-direnv}/share/nix-direnv/direnvrc";
+  BATS_LIB_PATH = lib.strings.makeSearchPath "" [
+    test_pkgs.bats-support
+    test_pkgs.bats-assert
   ];
+  packages =
+    (builtins.attrValues {
+      inherit (pkgs)
+        bats
+        direnv
+        shellcheck
+        ;
+    })
+    ++ (builtins.attrValues (lib.attrsets.filterAttrs (name: _val: name != "direnv-stdlib") test_pkgs))
+    ++ lib.optionals (treefmt != null) [ treefmt ];
 }

test-runner.nix

@@ -0,0 +1,54 @@
+{
+  bash,
+  bats,
+  callPackage,
+  coreutils,
+  direnv,
+  fetchurl,
+  findutils,
+  gnugrep,
+  lib,
+  nix-direnv,
+  nixVersions,
+  writeShellScriptBin,
+}:
+let
+  direnv-stdlib = fetchurl {
+    url = "https://raw.githubusercontent.com/direnv/direnv/refs/tags/v2.37.1/stdlib.sh";
+    hash = "sha256-MMM04OXhqS/rRSuv8uh7CD70Z7CaGT63EtL/3LC08qM=";
+  };
+  bats-support = callPackage ./nix/bats-support.nix { };
+  bats-assert = callPackage ./nix/bats-assert.nix { };
+  mkTestRunner =
+    nixVersion:
+    writeShellScriptBin "test-runner-${nixVersion}" ''
+      set -e
+      export PATH=${
+        lib.makeBinPath [
+          bash
+          direnv
+          nixVersions.${nixVersion}
+          coreutils
+          findutils
+          gnugrep
+        ]
+      }
+      export DIRENV_STDLIB=${direnv-stdlib}
+      export DIRENVRC="${nix-direnv}/share/nix-direnv/direnvrc"
+      export BATS_LIB_PATH="${bats-support}:${bats-assert}"
+
+      echo run unittest
+      ${lib.getExe' bats "bats"} -x --verbose-run tests/
+    '';
+  test-runner-stable = mkTestRunner "stable";
+  test-runner-latest = mkTestRunner "latest";
+in
+{
+  inherit
+    bats-support
+    bats-assert
+    direnv-stdlib
+    test-runner-stable
+    test-runner-latest
+    ;
+}

tests/bash/test_versions.bats

@@ -0,0 +1,23 @@
+{ fetchFromGitHub, stdenv }:
+stdenv.mkDerivation {
+  name = "bats-assert";
+  version = "2.1.0+";
+  src = fetchFromGitHub {
+    owner = "bats-core";
+    repo = "bats-assert";
+    rev = "912a98804efd34f24d5eae1bf97ee622ca770e9"; # master 8/7/2025
+    hash = "sha256-gp52V4mAiT+Lod2rvEMLhi0Y7AdQQTFCHcNgb8JEKXE=";
+  };
+
+  dontBuild = true;
+  installPhase = ''
+
+    # This looks funny
+    # but it means that you can use bats' built-in `bats_load_library` easily
+    # when setting $BATS_LIB_PATH to the string of the derivation.
+
+    mkdir -p $out/bats-assert
+    cp -r src $out/bats-assert/
+    cp load.bash $out/bats-assert
+  '';
+}

tests/default.nix

@@ -0,0 +1,24 @@
+{ stdenv, fetchFromGitHub }:
+
+stdenv.mkDerivation {
+  name = "bats-support";
+  version = "3.0+";
+  src = fetchFromGitHub {
+    owner = "bats-core";
+    repo = "bats-support";
+    rev = "0ad082d4590108684c68975ca517a90459f05cd0";
+    hash = "sha256-hkPAn12gQudboL9pDpQZhtaMhqyyj885tti4Gx/aun4=";
+  };
+
+  dontBuild = true;
+  installPhase = ''
+
+    # This looks funny
+    # but it means that you can use bats' built-in `bats_load_library` easily
+    # when setting $BATS_LIB_PATH to the string of the derivation.
+
+    mkdir -p $out/bats-support
+    cp -r src $out/bats-support/
+    cp load.bash $out/bats-support/
+  '';
+}