Add comprehensive unit tests for backend services and controllers

- Add API.Tests xUnit project with Moq and EF Core InMemory
- Add AgeGroupService tests (CRUD operations, edge cases)
- Add RegistrationKeyService tests (CRUD + DeleteOldRegistrationKeys)
- Add AgeGroupController tests (all endpoints with mocked service)
- Add PlunkEmailSender tests (HTTP client mocking, payload verification)
- Add Mapper tests (AltersgruppeMapper, RegistrationKeyMapper)

https://claude.ai/code/session_01Kv7Mp2c9FKsHEgQe4BoftH

API.Tests/Controllers/AgeGroupControllerTests.cs

@@ -0,0 +1,184 @@
+using API.Controllers;
+using API.Models.Internal.Altersgruppen;
+using API.Repository.AgeGroupRepo;
+using Microsoft.AspNetCore.Mvc;
+using Moq;
+
+namespace API.Tests.Controllers;
+
+public class AgeGroupControllerTests
+{
+    private readonly Mock<IAgeGroupService> _mockService;
+    private readonly AgeGroupController _controller;
+
+    public AgeGroupControllerTests()
+    {
+        _mockService = new Mock<IAgeGroupService>();
+        _controller = new AgeGroupController(_mockService.Object);
+    }
+
+    [Fact]
+    public async Task GetAll_ReturnsOkWithAllGroups()
+    {
+        // Arrange
+        var groups = new List<AltersGruppe>
+        {
+            new AltersGruppe { Id = "1", Name = "U10", StartingAge = 8, EndingAge = 10 },
+            new AltersGruppe { Id = "2", Name = "U12", StartingAge = 10, EndingAge = 12 }
+        };
+        _mockService.Setup(s => s.GetAllAsync()).ReturnsAsync(groups);
+
+        // Act
+        var result = await _controller.GetAll();
+
+        // Assert
+        var okResult = Assert.IsType<OkObjectResult>(result);
+        var returnedGroups = Assert.IsType<List<AltersGruppe>>(okResult.Value);
+        Assert.Equal(2, returnedGroups.Count);
+    }
+
+    [Fact]
+    public async Task GetAll_EmptyList_ReturnsOkWithEmptyList()
+    {
+        // Arrange
+        _mockService.Setup(s => s.GetAllAsync()).ReturnsAsync(new List<AltersGruppe>());
+
+        // Act
+        var result = await _controller.GetAll();
+
+        // Assert
+        var okResult = Assert.IsType<OkObjectResult>(result);
+        var returnedGroups = Assert.IsType<List<AltersGruppe>>(okResult.Value);
+        Assert.Empty(returnedGroups);
+    }
+
+    [Fact]
+    public async Task GetOne_ExistingId_ReturnsOkWithGroup()
+    {
+        // Arrange
+        var group = new AltersGruppe { Id = "123", Name = "U14", StartingAge = 12, EndingAge = 14 };
+        _mockService.Setup(s => s.GetAsync("123")).ReturnsAsync(group);
+
+        // Act
+        var result = await _controller.GetOne("123");
+
+        // Assert
+        var okResult = Assert.IsType<OkObjectResult>(result);
+        var returnedGroup = Assert.IsType<AltersGruppe>(okResult.Value);
+        Assert.Equal("U14", returnedGroup.Name);
+    }
+
+    [Fact]
+    public async Task GetOne_NonExistingId_ReturnsNotFound()
+    {
+        // Arrange
+        _mockService.Setup(s => s.GetAsync("nonexistent")).ReturnsAsync((AltersGruppe?)null);
+
+        // Act
+        var result = await _controller.GetOne("nonexistent");
+
+        // Assert
+        Assert.IsType<NotFoundResult>(result);
+    }
+
+    [Fact]
+    public async Task Create_ValidGroup_ReturnsCreatedAtAction()
+    {
+        // Arrange
+        var ingoingGroup = new AltersGruppeIngoing { Name = "U16", StartingAge = 14, EndingAge = 16 };
+        var createdGroup = new AltersGruppe { Id = "new-id", Name = "U16", StartingAge = 14, EndingAge = 16 };
+
+        _mockService.Setup(s => s.CreateAsync(It.IsAny<AltersGruppe>())).ReturnsAsync(createdGroup);
+
+        // Act
+        var result = await _controller.Create(ingoingGroup);
+
+        // Assert
+        var createdResult = Assert.IsType<CreatedAtActionResult>(result);
+        Assert.Equal(nameof(AgeGroupController.GetOne), createdResult.ActionName);
+
+        var returnedGroup = Assert.IsType<AltersGruppe>(createdResult.Value);
+        Assert.Equal("U16", returnedGroup.Name);
+        Assert.Equal("new-id", createdResult.RouteValues?["Id"]);
+    }
+
+    [Fact]
+    public async Task Update_ExistingGroup_ReturnsOkWithUpdatedGroup()
+    {
+        // Arrange
+        var ingoingGroup = new AltersGruppeIngoing { Name = "U16 Updated", StartingAge = 15, EndingAge = 16 };
+        var updatedGroup = new AltersGruppe { Id = "123", Name = "U16 Updated", StartingAge = 15, EndingAge = 16 };
+
+        _mockService.Setup(s => s.UpdateAsync("123", It.IsAny<AltersGruppe>())).ReturnsAsync(updatedGroup);
+
+        // Act
+        var result = await _controller.Update("123", ingoingGroup);
+
+        // Assert
+        var okResult = Assert.IsType<OkObjectResult>(result);
+        var returnedGroup = Assert.IsType<AltersGruppe>(okResult.Value);
+        Assert.Equal("U16 Updated", returnedGroup.Name);
+        Assert.Equal(15, returnedGroup.StartingAge);
+    }
+
+    [Fact]
+    public async Task Update_NonExistingGroup_ReturnsNotFound()
+    {
+        // Arrange
+        var ingoingGroup = new AltersGruppeIngoing { Name = "U16 Updated", StartingAge = 15, EndingAge = 16 };
+        _mockService.Setup(s => s.UpdateAsync("nonexistent", It.IsAny<AltersGruppe>())).ReturnsAsync((AltersGruppe?)null);
+
+        // Act
+        var result = await _controller.Update("nonexistent", ingoingGroup);
+
+        // Assert
+        Assert.IsType<NotFoundResult>(result);
+    }
+
+    [Fact]
+    public async Task Delete_ExistingGroup_ReturnsNoContent()
+    {
+        // Arrange
+        var group = new AltersGruppe { Id = "123", Name = "U18", StartingAge = 16, EndingAge = 18 };
+        _mockService.Setup(s => s.DeleteAsync("123")).ReturnsAsync(group);
+
+        // Act
+        var result = await _controller.Delete("123");
+
+        // Assert
+        Assert.IsType<NoContentResult>(result);
+    }
+
+    [Fact]
+    public async Task Delete_NonExistingGroup_ReturnsNotFound()
+    {
+        // Arrange
+        _mockService.Setup(s => s.DeleteAsync("nonexistent")).ReturnsAsync((AltersGruppe?)null);
+
+        // Act
+        var result = await _controller.Delete("nonexistent");
+
+        // Assert
+        Assert.IsType<NotFoundResult>(result);
+    }
+
+    [Fact]
+    public async Task Create_ServiceIsCalled_WithCorrectParameters()
+    {
+        // Arrange
+        var ingoingGroup = new AltersGruppeIngoing { Name = "U20", StartingAge = 18, EndingAge = 20 };
+        var createdGroup = new AltersGruppe { Id = "new-id", Name = "U20", StartingAge = 18, EndingAge = 20 };
+
+        _mockService.Setup(s => s.CreateAsync(It.IsAny<AltersGruppe>())).ReturnsAsync(createdGroup);
+
+        // Act
+        await _controller.Create(ingoingGroup);
+
+        // Assert
+        _mockService.Verify(s => s.CreateAsync(It.Is<AltersGruppe>(g =>
+            g.Name == "U20" &&
+            g.StartingAge == 18 &&
+            g.EndingAge == 20
+        )), Times.Once);
+    }
+}