Dotnet Test Doubles

using Bogus;

public sealed class GroupMother
{
    private readonly Faker _faker;

    public GroupMother(int seed = 666)
    {
        _faker = new Faker { Random = new Randomizer(seed) };
    }

    public Group Create()
    {
        return Group.Create(
            id: _faker.Random.Guid(),
            name: _faker.Commerce.ProductName(),
            type: _faker.PickRandom<GroupType>()
        );
    }
}

public class CreateGroupCommandHandlerTests
{
    private readonly Fixture _fixture;

    public CreateGroupCommandHandlerTests()
    {
        _fixture = new Fixture();
    }

    [Fact(Timeout = CancellationTokenForTest.ShortTimeout)] 
    public async Task Should_CreateGroup_When_RequestIsValid()
    {
        // Arrange
        var secretName = _fixture.Create<string>();
        var secretValue = _fixture.Create<string>();
        // ...
    }
}

// Arrange
_repository
    .GetGroupByIdAsync(Arg.Any<Guid>(), Arg.Any<CancellationToken>())
    .Returns(GroupMother.Create(id: expectedId));

// Arrange
var logger = Substitute.For<ILogger<CreateGroupCommandHandler>>();

// Act
await _sut.Handle(command, CancellationToken.None);

// Assert - Verify logger was called
logger.Received(1).Log(
    LogLevel.Information,
    Arg.Any<EventId>(),
    Arg.Is<object>(o => o.ToString()!.Contains("Creating group")),
    Arg.Any<Exception>(),
    Arg.Any<Func<object, Exception?, string>>());

// Arrange
_repository
    .GetGroupByIdAsync(groupId, Arg.Any<CancellationToken>())
    .Returns(group);

// Act
var actual = await _sut.Handle(query, CancellationToken.None);

// Assert
await _repository.Received(1).GetGroupByIdAsync(groupId, Arg.Any<CancellationToken>());

// Setup WireMock
_wireMock
    .Given(Request.Create()
        .WithPath("/secrets/my-secret")
        .UsingGet())
    .RespondWith(Response.Create()
        .WithStatusCode(200)
        .WithBodyAsJson(new { value = "secret-value" }));

// Test HTTP client
var response = await _httpClient.GetAsync("/secrets/my-secret");

// Create mock
var repository = Substitute.For<IEnvilderRepository>();

// Setup return value
repository
    .GetGroupByIdAsync(groupId, Arg.Any<CancellationToken>())
    .Returns(group);

// Verify call
await repository.Received(1).GetGroupByIdAsync(groupId, Arg.Any<CancellationToken>());

// Verify NOT called
await repository.DidNotReceive().DeleteGroup(Arg.Any<Group>());

// Any argument
repository.GetGroupByIdAsync(Arg.Any<Guid>(), Arg.Any<CancellationToken>());

// Specific value
repository.GetGroupByIdAsync(specificId, Arg.Any<CancellationToken>());

// Conditional matching
repository.GetGroupByIdAsync(
    Arg.Is<Guid>(id => id != Guid.Empty),
    Arg.Any<CancellationToken>());

public sealed class GroupMother
{
    private readonly Faker _faker;

    public GroupMother(int seed = 666)
    {
        _faker = new Faker { Random = new Randomizer(seed) };
    }

    public Group Create(
        Guid? id = null,
        string? name = null,
        GroupType? type = null)
    {
        return Group.Create(
            id: id ?? _faker.Random.Guid(),
            name: name ?? _faker.Commerce.ProductName(),
            type: type ?? _faker.PickRandom<GroupType>()
        );
    }

    public IEnumerable<Group> CreateMany(int count = 10)
    {
        for (var i = 0; i < count; i++)
        {
            yield return Create();
        }
    }
}