refactor(clanServices): add example of eval test

clanServices/flake-module.nix

@@ -1,8 +1,5 @@
-{ self, lib, ... }:
 {
-  clan.inventory.modules = {
-    zerotier-redux = lib.modules.importApply ./zerotier-redux/default.nix {
-      inherit (self) packages;
-    };
-  };
+  imports = [
+    ./zerotier-redux/flake-module.nix
+  ];
 }

clanServices/zerotier-redux/flake-module.nix

@@ -0,0 +1,41 @@
+{
+  self,
+  lib,
+  inputs,
+  ...
+}:
+let
+  inputOverrides = builtins.concatStringsSep " " (
+    builtins.map (input: " --override-input ${input} ${inputs.${input}}") (builtins.attrNames inputs)
+  );
+
+  module = lib.modules.importApply ./default.nix {
+    inherit (self) packages;
+  };
+in
+{
+  clan.inventory.modules = {
+    zerotier-redux = module;
+  };
+  perSystem =
+    { system, pkgs, ... }:
+    {
+      legacyPackages.eval-tests-zerotier-redux = import ./tests/eval-tests.nix {
+        inherit lib module;
+        inherit (self) clanLib;
+      };
+      checks = {
+        "eval-tests-zerotier-redux" = pkgs.runCommand "tests" { nativeBuildInputs = [ pkgs.nix-unit ]; } ''
+          export HOME="$(realpath .)"
+
+          nix-unit --eval-store "$HOME" \
+            --extra-experimental-features flakes \
+            --show-trace \
+            ${inputOverrides} \
+            --flake ${self}#legacyPackages.${system}.eval-tests-zerotier-redux
+
+          touch $out
+        '';
+      };
+    };
+}

clanServices/zerotier-redux/tests/eval-tests.nix

@@ -0,0 +1,53 @@
+{
+  module,
+  clanLib,
+  ...
+}:
+let
+  testFlake = clanLib.buildClan {
+    # Point to the folder of the module
+    # TODO: make this optional in buildClan
+    directory = ./..;
+
+    # Create some test machines
+    machines.jon = {
+      nixpkgs.hostPlatform = "x86_64-linux";
+    };
+    machines.sara = {
+      nixpkgs.hostPlatform = "x86_64-linux";
+    };
+
+    # Register the module for the test
+    inventory.modules.zerotier-redux = module;
+
+    # Use the module in the test
+    inventory.instances = {
+      "zero" = {
+        module.name = "zerotier-redux";
+
+        roles.peer.machines.jon = { };
+      };
+    };
+  };
+  # NOTE:
+  # If you wonder why 'self-zerotier-redux':
+  # A local module has prefix 'self', otherwise it is the name of the 'input'
+  # The rest is the name of the service as in the instance 'module.name';
+  #
+  # -> ${module.input}-${module.name}
+  # In this case it is 'self-zerotier-redux'
+  # This is usually only used internally, but we can use it to test the evaluation of service module in isolation
+  # evaluatedService =
+  #   testFlake.clanInternals.inventoryClass.distributedServices.importedModulesEvaluated.self-zerotier-redux.config;
+in
+{
+  test_simple = {
+    inherit testFlake;
+
+    expr = {
+    };
+    expected = {
+
+    };
+  };
+}