Likeness - polishing and packaging

问题:

I'm using Ploeh.SemanticComparison's Likeness as a way to effectively express intended outputs of a mapping process (as described in Mark Seemann's excellent Advanced Unit Testing course on PluralSight).

I'm testing some data has mapped correctly, which looks like this:

[Theory, AutoData]
static void ShouldYieldIdentifierUpdatedEvent( Vendor sut, string name, string version, Guid id )
{
    var result = sut.SyncProduct( name, version, id );

    var expected = new { ProductId = id, Name = name, Version = version };
    expected.AsSource().OfLikeness<NewMappingsEvent>()
        .Without( y => y.ProgrammaticIdentifier)
        .ShouldEqual(result);
}

However, I'm not happy:-

1. I want to apply a name to the Resemblance (i.e. name my .Without( y => y.ProgrammaticIdentifier) customization)
2. I've lost the symmetry with Assert.Equal( expected,actual, comparer) (but I definitely need the error message from ShouldEqual)

Is there a cleaner way to express this within the expressed constraints?

回答1:

If you had an Assertion helper class called AssertResemblance (like [4]), and a static helper like [1] in scope you could say it like:

var expected = new { ProductId = id, Name = name, Version = version };
AssertResemblance.Like( expected, result, WithoutProgrammaticIdentifier );

Or if you had an extension method like [2], you could do it like:

AssertResemblance.Like( expected,result,x=>x.WithoutProgrammaticIdentifier());

Or you could have the best of both worlds (no noise as in the first snippet) yet naming the Resemblance (by having the actual impl in an extension method) by implementing a local static helper in terms of the extension method ([2]) as in [3].

---

[1]

public static Likeness<T, NewMappingsEvent> WithoutProgrammaticIdentifier<T>( Likeness<T, NewMappingsEvent> that )
{
    return that.Without( x => x.ProgrammaticIdentifier );
}

[2]

static class NewMappingsEventResemblances
{
    public static Likeness<T, NewMappingsEvent> WithoutProgrammaticIdentifier<T>( this Likeness<T, NewMappingsEvent> that )
    {
        return that.Without( x => x.ProgrammaticIdentifier );
    }
}

[3]

static Likeness<T, NewMappingsEvent> WithoutProgrammaticIdentifier<T>( Likeness<T, NewMappingsEvent> that )
{
    return that.WithoutProgrammaticIdentifier();
}

[4]

static class AssertResemblance
{
    public static void Like<T, T2>( T expected, T2 actual )
    {
        Like( expected, actual, x => x );
    }

    public static void Like<T, T2>( T expected, T2 actual, Func<Likeness<T, T2>, Likeness<T, T2>> configureLikeness )
    {
        var likeness = expected.AsSource().OfLikeness<T2>();
        configureLikeness( likeness ).ShouldEqual( actual );
    }
}