3 files changed, 61 insertions, 13 deletions
diff --git a/flake.nix b/flake.nix
index f28d40b..cf39e80 100644
--- a/flake.nix
+++ b/flake.nix
@@ -86,24 +86,38 @@
   } @ attrs: let
     system = "x86_64-linux";
     pkgs = nixpkgs.legacyPackages.${system};
+    nixos-lib = import (nixpkgs + "/nixos/lib") {};
     pkgsUnstable = nixpkgs-unstable.legacyPackages.${system};
+
+    specialArgs =
+      attrs
+      // {
+        inherit pkgsUnstable nixpkgs-unstable nixos-lib extraModules;
+      };
+
+    extraModules = [
+      simple-nixos-mailserver.nixosModule
+      disko.nixosModules.default
+      impermanence.nixosModules.impermanence
+      agenix.nixosModules.default
+    ];
+
+    inherit (pkgs) lib;
+    tests = import ./tests.nix {inherit lib pkgs specialArgs;};
   in {
     nixosConfigurations."server1" = nixpkgs.lib.nixosSystem {
       system = "x86_64-linux";
-      specialArgs =
-        attrs
-        // {
-          inherit pkgsUnstable;
-        };
-      modules = [
-        ./modules/nixos
-        ./hosts/server1/configuration.nix
-        simple-nixos-mailserver.nixosModule
-        disko.nixosModules.default
-        impermanence.nixosModules.impermanence
-        agenix.nixosModules.default
-      ];
+      inherit specialArgs;
+      modules =
+        extraModules
+        ++ [
+          ./modules/nixos
+          ./hosts/server1/configuration.nix
+        ];
     };
+
+    checks."${system}" = tests;
+
     devShells."${system}" = {
       default = pkgs.mkShell {
         packages = with pkgs; [
diff --git a/tests.nix b/tests.nix
new file mode 100644
index 0000000..d91a9c9
--- /dev/null
+++ b/tests.nix
@@ -0,0 +1,28 @@
+{
+  pkgs,
+  lib,
+  specialArgs,
+}: let
+  # for `nix eval --file` (as it does not support args) use:
+  # ```
+  # specialArgs = {};
+  # pkgs = (builtins.getFlake "nixpkgs").legacyPackages."x86_64-linux";
+  # inherit (pkgs) lib;
+  # ```
+  # instead of the function arguments above.
+  importTests' = test: let
+    basename = builtins.baseNameOf test;
+    testName = builtins.baseNameOf (lib.strings.removeSuffix "/${basename}" "${builtins.toString test}");
+  in {
+    name = "${testName}";
+    value = pkgs.callPackage test specialArgs;
+  };
+
+  importTests = dir:
+    builtins.listToAttrs (builtins.map importTests' (
+      lib.fileset.toList (lib.fileset.fileFilter (file: file.name == "test.nix") dir)
+    ));
+
+  tests = importTests ./tests;
+in
+  tests
diff --git a/tests/README.md b/tests/README.md
new file mode 100644
index 0000000..2613f4a
--- /dev/null
+++ b/tests/README.md
@@ -0,0 +1,6 @@
+# Tests
+
+This directory tree mirrors the modules defined in the
+[modules](`../modules/`) directory.  Each module should have at least
+one test in the mirrored directory, effectively replacing the module's
+`default.nix` file.