Right approach to test convert-like methods

Suppose i have lots of classes like this (Foo1, Foo2 ..)

class Foo 
{
    public int F{get; set;}

    public Bar ConvertToBar ()
    {
        return new Bar(){ B = this.F*10 };
    }
}

all they have in common is ConvertToBar() method.

I have two approaches to unit-test this method:

1. Call convert to ConvertToBar () and check all it's properties (I have to do it in all tests for each Foo like class)

   Bar bar = foo.ConvertToBar (); Assert.AreEqual (expectedValue, bar.Property); ...

2. Write helper method that compares two Bar instances and then use it like this:

   Bar expectedBar = new Bar () Assert.True( barCompareMethod (expectedBar, foo.ConvertToBar ());

What will be the best way to write unit-test for 开发者_StackOverflow中文版this method?

Does it make sense for Bar itself to be IEquatable<Bar>? If so, I'd implement that in your production code, rather than having a helper method. Then you can just use Assert.AreEqual(expectedBar, actualBar).

As Jon Skeet suggests, implementing custom equality on Bar is a great idea as long as you understand how to steer clear of Equality Pollution.

For semantic comparison, you can use AutoFixture's SemanticComparison library, which would enable you to write a assertion like this:

var expected = bar1.AsSource().OfLikeness<Bar>();
expected.ShouldEqual(bar2);

The ShouldEqual method is a custom assertion that will compare each property (matched by name) and only succeed when all properties are equal; otherwise it will throw a descriptive exception.

I'm not sure there is a best way.

• the first is a bit more readable in my opinion. You may want to experiment with NUnit's property constaints

  Assert.That(someObject, Has.Property("Version").EqualTo("2.0"));

• the second is a bit more work in that you'd have to define Equals in the Bar classes (might be a problem if you do not have source edit access). But it would be preferable, if a large number of properties need to be asserted on.