Build DSL

When Create is too coarse, Build<T>() returns a composer you can configure before calling Create().

Example scenario

You are testing a component that reads ClientDto.Name and ClientDto.Age. You need to pin specific values for those properties while AutoFixture fills the rest — or leave some properties at their defaults.

Example

With — set property values:

var fixture = new Fixture();
var expectedName = fixture.Create<string>();

var client = fixture.Build<ClientDto>()
    .With(dto => dto.Name, expectedName)
    .With(dto => dto.Age, 42)
    .Create();

Assert.Equal(expectedName, client.Name);
Assert.Equal(42, client.Age);

Without — skip auto assignment:

var client = fixture.Build<ClientDto>()
    .Without(dto => dto.Age)
    .Create();

Assert.Equal(default, client.Age);

OmitAutoProperties — empty shell:

var client = fixture.Build<ClientDto>()
    .OmitAutoProperties()
    .Create();

Assert.Equal(string.Empty, client.Name);
Assert.Equal(default, client.Age);

How it works

• Build<T>() — returns an IPostprocessComposer<T> you chain before Create()
• With — overrides a property value on the final specimen
• Without — leaves a property at its default instead of auto-assigning
• OmitAutoProperties — skips all property assignment; only constructor parameters are filled

Use Build when business rules or test assertions require specific property values. See Refactoring a test for a graph constraint example.

Next steps

• Customizations
• Collections

API

• Fixture.Build