functionalddd.testing

FunctionalDDD.Testing

Testing utilities and FluentAssertions extensions for FunctionalDDD - Write expressive, maintainable tests for Railway-Oriented Programming patterns.

Installation

dotnet add package FunctionalDDD.Testing

Features

✅ FluentAssertions Extensions - Expressive assertions for Result<T>, Maybe<T>, and Error types
🏗️ Test Builders - Fluent builders for creating test data
🎭 Fake Implementations - In-memory fakes for repositories and infrastructure
📖 Readable Tests - Write tests that read like specifications
💡 IntelliSense Support - Discover test utilities through IntelliSense

Quick Start

Result Assertions

using FunctionalDdd.Testing;

[Fact]
public void Should_Return_Success()
{
    var result = EmailAddress.TryCreate("[e-mail]");

    result.Should()
        .BeSuccess()
        .Which.Value.Should().Contain("@");
}

[Fact]
public void Should_Return_NotFound_Error()
{
    var result = _repository.GetByIdAsync(userId, ct);

    result.Should()
        .BeFailureOfType<NotFoundError>()
        .Which.Should()
        .HaveDetail("User not found");
}

Validation Error Assertions

[Fact]
public void Should_Have_Multiple_Validation_Errors()
{
    var result = CreateUser("", "invalid-email", 15);

    result.Should()
        .BeFailureOfType<ValidationError>()
        .Which.Should()
        .HaveFieldCount(3)
        .And.HaveFieldError("firstName")
        .And.HaveFieldError("email")
        .And.HaveFieldErrorWithDetail("age", "Must be 18 or older");
}

Maybe Assertions

[Fact]
public void Should_Have_Value()
{
    var maybe = Maybe.From("hello");

    maybe.Should()
        .HaveValue()
        .Which.Should().Be("hello");
}

[Fact]
public void Should_Be_None()
{
    var maybe = Maybe.None<string>();

    maybe.Should().BeNone();
}

Test Builders

[Fact]
public void Should_Handle_NotFound()
{
    var result = ResultBuilder.NotFound<User>("User not found");

    result.Should()
        .BeFailureOfType<NotFoundError>();
}

[Fact]
public void Should_Build_Complex_Validation_Error()
{
    var error = ValidationErrorBuilder.Create()
        .WithFieldError("email", "Email is required")
        .WithFieldError("email", "Invalid email format")
        .WithFieldError("age", "Must be 18 or older")
        .Build();

    error.Should()
        .HaveFieldCount(2)
        .And.HaveFieldErrorWithDetail("email", "Email is required");
}

Fake Repository

public class UserServiceTests
{
    private readonly FakeRepository<User, UserId> _fakeRepository;
    private readonly UserService _sut;

    public UserServiceTests()
    {
        _fakeRepository = new FakeRepository<User, UserId>();
        _sut = new UserService(_fakeRepository);
    }

    [Fact]
    public async Task Should_Save_User_And_Publish_Event()
    {
        // Arrange
        var command = new CreateUserCommand("John", "Doe", "[e-mail]");

        // Act
        var result = await _sut.CreateUserAsync(command, CancellationToken.None);

        // Assert
        result.Should().BeSuccess();
        
        _fakeRepository.Exists(result.Value.Id).Should().BeTrue();
        _fakeRepository.PublishedEvents.Should().ContainSingle()
            .Which.Should().BeOfType<UserCreatedEvent>();
    }
}

API Reference

Result Assertions

Method	Description
BeSuccess()	Asserts the result is a success
BeFailure()	Asserts the result is a failure
BeFailureOfType<TError>()	Asserts the result failed with a specific error type
HaveValue(expected)	Asserts the success value equals the expected value
HaveValueMatching(predicate)	Asserts the success value satisfies a predicate

Error Assertions

Method	Description
HaveCode(code)	Asserts the error has the specified code
HaveDetail(detail)	Asserts the error has the specified detail message
HaveDetailContaining(substring)	Asserts the error detail contains a substring
BeOfType<TError>()	Asserts the error is of a specific type

ValidationError Assertions

Method	Description
HaveFieldError(fieldName)	Asserts the validation error contains a field error
HaveFieldErrorWithDetail(field, detail)	Asserts a field has a specific error detail
HaveFieldCount(count)	Asserts the number of field errors

Maybe Assertions

Method	Description
HaveValue()	Asserts the Maybe has a value
BeNone()	Asserts the Maybe has no value
HaveValueEqualTo(expected)	Asserts the value equals the expected value

Benefits

Before	After
result.IsSuccess.Should().BeTrue()	result.Should().BeSuccess()
result.Error.Should().BeOfType<NotFoundError>()	result.Should().BeFailureOfType<NotFoundError>()
maybe.HasValue.Should().BeTrue()	maybe.Should().HaveValue()
Manual repository setup with mocks	new FakeRepository<User, UserId>()

Advantages:

• ✂️ 60% Less Code - More concise assertions
• 💬 Better Error Messages - Detailed failure descriptions
• 💡 IntelliSense Guided - Discover test patterns through IDE
• 📖 Readable Tests - Tests read like specifications
• 🔒 Type Safe - Compiler-enforced correctness

Related Packages

• FunctionalDDD.RailwayOrientedProgramming - Core Result/Maybe types
• FunctionalDDD.DomainDrivenDesign - DDD building blocks

License

MIT

Contributing

Contributions are welcome! See the main repository for guidelines.