Register, Freeze, and Inject

Use Inject when you already have the object. Use Freeze when AutoFixture should create it once and reuse it. Use Register when you control how each request is built.

Example scenario

You are testing code that resolves the same ClientDto from multiple places in an object graph. You need one shared instance — or a factory that always returns a known string.

Example

Register — factory for a type:

var fixture = new Fixture();
fixture.Register(() => "registered");

Assert.Equal("registered", fixture.Create<string>());

Freeze — one shared instance:

var frozen = fixture.Freeze<ClientDto>();

var resolved = fixture.Create<ClientDto>();

Assert.Same(frozen, resolved);

Inject — exact instance:

var injected = new ClientDto { Name = "injected", Age = 1 };
fixture.Inject(injected);

Assert.Same(injected, fixture.Create<ClientDto>());

How it works

• Register<T>(Func<T>) — replaces how T is created on every request
• Freeze<T>() — creates T once, then injects that instance so later requests on this fixture reuse it
• Inject<T>(T) — supplies a specific instance for all later requests of that type on this fixture

See Customizations.

Next steps

• Customizations
• AutoMoq
• AutoNSubstitute
• AutoFakeItEasy
• FAQ