services: update hello-world readme and tests

clanServices/hello-world/tests/eval-tests.nix

@@ -4,7 +4,7 @@
   ...
 }:
 let
-  testFlake = clanLib.clan {
+  testClan = clanLib.clan {
     self = { };
     # Point to the folder of the module
     # TODO: make this optional
@@ -33,10 +33,20 @@ let
   };
 in
 {
-  test_simple = {
-    config = testFlake.config;
+  /**
+    We highly advocate the usage of:
+    https://github.com/nix-community/nix-unit
 
-    expr = { };
-    expected = { };
+    If you use flake-parts you can use the native integration: https://flake.parts/options/nix-unit.html
+  */
+  test_simple = {
+    # Allows inspection via the nix-repl
+    # Ignored by nix-unit; it only looks at 'expr' and 'expected'
+    inherit testClan;
+
+    # Assert that jon has the
+    # configured greeting in 'environment.etc.hello.text'
+    expr = testClan.config.nixosConfigurations.jon.config.environment.etc."hello".text;
+    expected = "Good evening World!";
   };
 }