Add Tests

Add tests

Test what is engine-free: Service and Domain. UI/Level are not unit-tested. Reference: NoteServiceTests.cs. Stack is NUnit + Moq (already in tests/Game.Tests/Game.Tests.csproj).

Rules:

1. Location mirrors source: src/Game/<Module>/Service/<X>.cs → tests/Game.Tests/<Module>/Service/<X>Tests.cs. Test namespace: Game.Tests.<Module>.<Layer>.

2. Mock Common interfaces with Moq — IJsonStateFileHandlerService, IRandomGeneratorService, IIdService, etc. Use real in-memory repositories (SingleRepository<T> / CollectionRepository<...>) when convenient.

3. Structure: [TestFixture], [SetUp] to build the system under test, one [Test] per behavior. Assert with Assert.That(actual, Is.EqualTo(...)).

4. Cover: happy path, edge/empty cases, and that the service calls its dependencies correctly (mock.Verify(...)). When a method returns a file/IO result, assert the returned FileError/bool and the resulting in-memory state.

5. No redundant tests — don't test framework code, trivial getters, or Godot behavior. Keep tests current with the code.

6. After writing, run the verify skill.

Example shape:

[SetUp] public void SetUp() { _dep = new Mock<IDep>(); _sut = new XService(_repo, _dep.Object); }

[Test]
public void DoesThing()
{
    _dep.Setup(d => d.Call(It.IsAny<...>())).Returns(...);
    var result = _sut.DoThing();
    Assert.That(result, Is.EqualTo(...));
    _dep.Verify(d => d.Call(It.IsAny<...>()), Times.Once);
}