test: fix flaky and silent assertions in unit tests (#396)

- Replace if-guarded 201 assertion with unconditional BeOfType and add
  RouteValues squadNumber value check (PlayerControllerTests)
- Inject TimeProvider into PlayerRequestModelValidator to eliminate
  DateTime.UtcNow coupling
- Add FakeTimeProvider in PlayerValidatorTests and pin DateOfBirthToday
  to a fixed clock shared with the validator

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: nanotaboada

src/Dotnet.Samples.AspNetCore.WebApi/Validators/PlayerRequestModelValidator.cs

@@ -18,9 +18,13 @@ public class PlayerRequestModelValidator : AbstractValidator<PlayerRequestModel>
 {
     private readonly IPlayerRepository _playerRepository;
 
-    public PlayerRequestModelValidator(IPlayerRepository playerRepository)
+    public PlayerRequestModelValidator(
+        IPlayerRepository playerRepository,
+        TimeProvider? timeProvider = null
+    )
     {
         _playerRepository = playerRepository;
+        var clock = timeProvider ?? TimeProvider.System;
 
         RuleFor(player => player.FirstName).NotEmpty().WithMessage("FirstName is required.");
 
@@ -45,7 +49,7 @@ public PlayerRequestModelValidator(IPlayerRepository playerRepository)
             () =>
             {
                 RuleFor(player => player.DateOfBirth)
-                    .Must(date => date!.Value.Date < DateTime.UtcNow.Date)
+                    .Must(date => date!.Value.Date < clock.GetUtcNow().Date)
                     .WithMessage("DateOfBirth must be a date in the past.")
                     .Must(date =>
                         date!.Value.Date >= new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)

test/Dotnet.Samples.AspNetCore.WebApi.Tests/Unit/PlayerControllerTests.cs

@@ -146,14 +146,12 @@ public async Task Post_Players_NonExisting_Returns201Created()
                 ),
             Times.Once
         );
-        if (result is CreatedAtRoute<PlayerResponseModel> httpResult)
-        {
-            httpResult.Should().NotBeNull().And.BeOfType<CreatedAtRoute<PlayerResponseModel>>();
-            httpResult.StatusCode.Should().Be(StatusCodes.Status201Created);
-            httpResult.Value.Should().BeEquivalentTo(response);
-            httpResult.RouteName.Should().Be("RetrieveBySquadNumber");
-            httpResult.RouteValues.Should().NotBeNull().And.ContainKey("squadNumber");
-        }
+        var httpResult = result.Should().BeOfType<CreatedAtRoute<PlayerResponseModel>>().Subject;
+        httpResult.StatusCode.Should().Be(StatusCodes.Status201Created);
+        httpResult.Value.Should().BeEquivalentTo(response);
+        httpResult.RouteName.Should().Be("RetrieveBySquadNumber");
+        httpResult.RouteValues.Should().NotBeNull().And.ContainKey("squadNumber");
+        httpResult.RouteValues!["squadNumber"].Should().Be(response.Dorsal);
     }
 
     /* -------------------------------------------------------------------------

test/Dotnet.Samples.AspNetCore.WebApi.Tests/Unit/PlayerValidatorTests.cs

@@ -9,12 +9,18 @@ namespace Dotnet.Samples.AspNetCore.WebApi.Tests.Unit;
 
 public class PlayerValidatorTests
 {
+    private sealed class FakeTimeProvider(DateTimeOffset utcNow) : TimeProvider
+    {
+        public override DateTimeOffset GetUtcNow() => utcNow;
+    }
+
     private static PlayerRequestModelValidator CreateValidator(
-        Mock<IPlayerRepository>? repositoryMock = null
+        Mock<IPlayerRepository>? repositoryMock = null,
+        TimeProvider? timeProvider = null
     )
     {
         var mock = repositoryMock ?? new Mock<IPlayerRepository>();
-        return new PlayerRequestModelValidator(mock.Object);
+        return new PlayerRequestModelValidator(mock.Object, timeProvider);
     }
 
     /* -------------------------------------------------------------------------
@@ -213,9 +219,11 @@ public async Task ValidateAsync_DateOfBirthInFuture_ReturnsValidationError()
     public async Task ValidateAsync_DateOfBirthToday_ReturnsValidationError()
     {
         // Arrange
+        var fixedNow = new DateTimeOffset(2000, 1, 1, 0, 0, 0, TimeSpan.Zero);
+        var timeProvider = new FakeTimeProvider(fixedNow);
         var request = PlayerFakes.MakeRequestModelForCreate();
-        request.DateOfBirth = DateTime.UtcNow.Date; // rule: strictly < UtcNow.Date
-        var validator = CreateValidator();
+        request.DateOfBirth = fixedNow.Date; // same "today" the validator sees
+        var validator = CreateValidator(timeProvider: timeProvider);
 
         // Act
         var result = await validator.ValidateAsync(request);