Fabricate 0.1.0

Fabricate

A .NET source generator that creates builder pattern classes for test projects. Define what a valid object looks like once, get fluent With methods for free.

Why?

Test setup is verbose. You create objects, set properties, and repeat. Fabricate lets you define a valid instance of your domain object once, then override only what matters per test — surfacing intent and reducing noise.

Installation

dotnet add package Fabricate

Note: Add this only to your test project. Use PrivateAssets="all" to prevent it leaking to production.

Quick Start

Given a domain model:

public class Patient
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string? MiddleName { get; set; }
}

Create a builder:

using Fabricate;

[Fabricate<Patient>]
public partial class PatientBuilder
{
    private static partial Patient ValidInstance() => new()
    {
        Name = "John Doe",
        Age = 30,
        MiddleName = null
    };
}

Use it in tests:

// Default valid instance
Patient patient = new PatientBuilder().Build();

// Override specific values
Patient child = new PatientBuilder().WithAge(5).Build();

// Implicit conversion
Patient patient = new PatientBuilder().WithName("Jane");

// Factory shorthand (auto-generated)
Patient patient = A.Patient.WithName("Quick").Build();

Features

Supported Types

• Classes, records, structs, readonly structs, record structs
• Constructor parameters (auto-detected)
• Init-only properties
• Nullable properties (generates Without methods)
• Collections (params arrays)
• Inherited properties (flattened)

Smart With Method Naming

• BCL types (string, int, DateTime, etc.) → WithPropertyName(T value)
• Custom types (unique) → With(T value) — the type is self-describing
• Custom types (duplicated) → WithPropertyName(T value) — disambiguate

Factory Class

A static A class is auto-generated with properties for each builder:

A.Patient           // → new PatientBuilder()
A.Appointment       // → new AppointmentBuilder()

Customize the name with an assembly attribute:

[assembly: FabricateFactory("Given")]
// Now use: Given.Patient.WithName("test")

Nullable Support

// Set a nullable value
builder.WithMiddleName("Marie")

// Clear a nullable value
builder.WithoutMiddleName()

Collections

// Set multiple values
builder.WithAllergies("Peanuts", "Shellfish")

// Set single value
builder.WithAllergies("Dust")

Diagnostics

Extending the Factory

Since A is a partial class, extend it in your test project:

public static partial class A
{
    public static PatientBuilder AdultPatient => Patient.WithAge(30);
    public static PatientBuilder ChildPatient => Patient.WithAge(5);
}

License

MIT