Why doesn't simple test pass using AutoFixture Freeze, SemanticComparison Likeness and CreateProxy?

问题

I'm trying to understand how to use the CreateProxy() feature of Likeness<T>() using two instances of a simple class.

public class Band
{
    public string Strings { get; set; }
    public string Brass { get; set; }
}

With the following test, I use a Fixture to Create<T> a Band instance with values for the two string properties.

[Fact]
public void Equality_Behaves_As_Expected()
{
    // arrange
    var fixture = new Fixture();
    fixture.Customize(new AutoMoqCustomization());

    var original = fixture.Create<Band>();
    //   Brass something like --> "Brass65756b89-d9f3-42f8-88fc-ab6de5ae65cd"
    //   Strings something like --> "Strings7439fa1b-014d-4544-8428-baea66858940"

    // act
    var dupe = new Band {Brass = original.Brass, 
                         Strings = original.Strings};
    //   Brass same as original's like --> "Brass65756b89-d9f3-42f8-88fc-ab6de5ae65cd"
    //   Strings same as original's like --> "Strings7439fa1b-014d-4544-8428-baea66858940"

I've tried many different assertions, but the crux of the matter seems to be that the CreateProxy method is not populating the properties of Band, so that even when I try to compare two instances of Band with the same property values, the instance from the CreateProxy method always has null values.

    // assert
    var likeness = dupe.AsSource().OfLikeness<Band>()
                       .Without(x => x.Brass).CreateProxy();
    //   Brass & String properties are null using dupe as source of likeness (!)

    //var likeness = original.AsSource().OfLikeness<Band>()
    //                       .Without(x => x.Brass).CreateProxy();
    //   Brass & String properties are null using original as source of likeness (!)

    //Assert.True(likeness.Equals(original)); // Fails
    //Assert.True(original.Equals(likeness)); // Fails

    // below are using FluentAssertions assembly
    //likeness.Should().Be(original);           // Fails (null properties)
    //original.Should().Be(likeness);           // Fails (null properties)
    //likeness.ShouldBeEquivalentTo(original);  // Fails (null properties)
    //original.ShouldBeEquivalentTo(likeness);  // Fails (null properties)
}

I've gotta be doing something wrong, but I've read everything I can find on the Ploeh blog and SO, and can't find an example suitably simple enough to compare to what I'm doing. Any ideas?

回答1:

If you assign the values on the proxied instance (after calling the CreateProxy method) the test passes:

[Fact]
public void Equality_Behaves_As_Expected()
{
    // AutoMoqCustomization is not necessary.
    var original = new Fixture().Create<Band>();

    var likeness = original
        .AsSource()
        .OfLikeness<Band>()
        .Without(x => x.Brass)
        .CreateProxy();

    likeness.Brass = "foo"; // Ignored.
    likeness.Strings = original.Strings;

    Assert.True(likeness.Equals(original));
    likeness.Should().Be(original);
    likeness.ShouldBeEquivalentTo(original);
}

Keep in mind that Likeness creates a proxy on the target type and only that type's instance overrides Equals.

Since the source type remains intact, the following assertions will not succeed:

Assert.True(original.Equals(likeness));
original.Should().Be(likeness);
original.ShouldBeEquivalentTo(likeness);

Update

From version 3.0.4 and above the values are automatically copied to the proxy instance (which means, likeness.Strings = original.Strings; is going to happen automatically).

来源：https://stackoverflow.com/questions/15470997/why-doesnt-simple-test-pass-using-autofixture-freeze-semanticcomparison-likene

标签

autofixture

semantic-comparison