test-data-builder-generator

Test Data Builder Generator

Generate fluent builders (and object mothers) so tests construct valid domain objects in one readable line, with only the fields that matter to each test made explicit.

Input — point it at your code

Works on a target: a class/file, folder, project, or GitHub URL. Find the types tests need and current setup pain: grep -rln "public class\|public record" --include=*.cs <target> and look at existing *Tests.cs for repeated new X { ... }.

Builder (sensible defaults + overrides)

public class OrderBuilder
{
    private Guid _customerId = Guid.NewGuid();
    private OrderStatus _status = OrderStatus.Pending;
    private readonly List<OrderLine> _lines = new() { new("SKU1", 1) };

    public OrderBuilder ForCustomer(Guid id) { _customerId = id; return this; }
    public OrderBuilder WithStatus(OrderStatus s) { _status = s; return this; }
    public OrderBuilder WithLines(params OrderLine[] l) { _lines.Clear(); _lines.AddRange(l); return this; }

    public Order Build() => Order.Create(_customerId, _lines).Value with { Status = _status };
    public static implicit operator Order(OrderBuilder b) => b.Build();
}

// readable: only what matters to THIS test is explicit
var order = new OrderBuilder().WithStatus(OrderStatus.Confirmed);

Object mother (named canonical cases)

public static class Orders
{
    public static Order Pending()   => new OrderBuilder();
    public static Order Confirmed() => new OrderBuilder().WithStatus(OrderStatus.Confirmed);
}

Builders vs AutoFixture

• Builders/mothers — explicit, readable, domain-aware; best when objects have invariants/relationships.
• AutoFixture — great for "I don't care about the values" cases; can combine with builders for the bits you do care about. The skill recommends based on how much the test depends on specific values.

Principles

• Default everything, override what the test cares about — that's what makes the test's intent obvious.
• Builders should produce valid objects (respect invariants/factories), not bypass them.
• Name canonical scenarios (object mothers) to kill duplication across tests.