Difference between Fact and Theory? - xUnit.net

Question

I'm new to xUnit.net and AutoFixture.

I'm currently working on a "testproject" to get familiar with xUnit.net and Autofixture. There is one little thing I don't understand.

What is the difference between [Fact] and [Theory, AutoMoqData]?

Could you please tell me if the following two pieces of code are equal? I'm asking this because the Test succeeds with both, but I want to learn it the right way.

[Fact] public void UpdateVersionWillUpdateCorrectlyInRepository() {     var fixture = new Fixture().Customize(new AutoMoqCustomization());     var contract = fixture.Create<VersionContract>();     var version = fixture.Create<Version>();      fixture.Freeze<Mock<IContractMapper>>()         .Setup(r => r.Map(contract)).Returns(version);      var repMock = fixture.Freeze<Mock<VersionRepository>>();      var sut = fixture.Create<VersionManagementService>();      sut.UpdateVersion(contract);      repMock.Verify(r => r.UpdateVersion(version)); } 

and

[Theory, AutoMoqData] public void UpdateVersionWillUpdateCorrectlyInRepository(     VersionContract contract,     Version version,     [Frozen]Mock<IContractMapper> mapMock,     [Frozen]Mock<VersionRepository> repMock,     VersionManagementService sut) {     mapMock.Setup(r => r.Map(contract)).Returns(version);      sut.UpdateVersion(contract);      repMock.Verify(r => r.UpdateVersion(version)); } 

What makes me think that there is a difference are the Keywords [Fact] and [Theory].

I'm assuming that the [Theory] Keywords tells the xUnit.net framework that the supplied data comes from somewhere, where somewhere is Autofixture. Whereas [Fact] tells xUnit nothing about the origin of the data and I need to build the objects manually.

Answer 1

Assuming that your [AutoMoqData] attribute looks something like this:

public class AutoMoqDataAttribute : AutoDataAttribute {     internal AutoMoqDataAttribute()         : base(new Fixture().Customize(new AutoMoqCustomization()))     {     } } 

Then, yes, those two tests are equivalent.

Both [Fact] and [Theory] attributes are defined by xUnit.net.

The [Fact] attribute is used by the xUnit.net test runner to identify a 'normal' unit test: a test method that takes no method arguments.

The [Theory] attribute, on the other, expects one or more DataAttribute instances to supply the values for a Parameterized Test's method arguments.

xUnit.net itself supplies various attributes that derive from DataAttribute: [InlineData], [ClassData], [PropertyData].

AutoFixture hooks into this extensibility point of xUnit.net by supplying the [AutoData] attribute. It can be used to make tests more declarative.