The intended usage of Assert.Equivalent is that you only put the things you care about in the expected value, and everything else is ignored. The easiest way to do this is not to use a concrete type for the expected value, but instead to use an anonymous value with just the property values you care about.

For example, if you have this class:

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

and you want to only validate the name without the age, you would do this:

var person = GetAPersonFromSomewhere();

Assert.Equivalent(new { FirstName = "Brad", LastName = "Wilson" }, person);

The other way you could handle this, if you want to use concrete types on both sides, is use Assert.Equal with your own comparison function:

var expected = new Person { FirstName = "Brad", LastName = "Wilson" };
var actual = new Person { FirstName = "Brad", LastName = "Wilson", Age = 123 };

Assert.Equal(
    expected,
    actual,
    (person1, person2) =>
        person1.FirstName == person2.FirstName &&
        person1.LastName == person2.LastName
);

Hi Brad and thanks for taking the time to read my post and write your replies!

In my scenario I'm comparing a complex object graph containing properties I need to exclude from comparison. Creating an anonymous object is a bit of an overkill.

Fluent Assertions does offer this functionality (see Selecting Members), alas it's not used in the project I'm working on.

We obviously don't have a fluent syntax from which to derive such exclusions, so any exclusion API would be something like a string based system such as TopLevel.SubLevel1.SubLevel2.PropertyName.

I'll leave this open to see how much uptake it gets from the community.