c# - How to Compare two objects in unit test?

Question

public class Student
{
    public string Name { get; set; }
    public int ID { get; set; }
}

...

var st1 = new Student
{
    ID = 20,
    Name = "ligaoren",
};

var st2 = new Student
{
    ID = 20,
    Name = "ligaoren",
};

Assert.AreEqual<Student>(st1, st2);// How to Compare two object in Unit test?

How to Compare two collection in Unitest?

Answer 1

What you are looking for is what in xUnit Test Patterns is called Test-Specific Equality.

While you can sometimes choose to override the Equals method, this may lead to Equality Pollution because the implementation you need to the test may not be the correct one for the type in general.

For example, Domain-Driven Design distinguishes between Entities and Value Objects, and those have vastly different equality semantics.

When this is the case, you can write a custom comparison for the type in question.

If you get tired doing this, AutoFixture's Likeness class offers general-purpose Test-Specific Equality. With your Student class, this would allow you to write a test like this:

[TestMethod]
public void VerifyThatStudentAreEqual()
{
    Student st1 = new Student();
    st1.ID = 20;
    st1.Name = "ligaoren";

    Student st2 = new Student();
    st2.ID = 20;
    st2.Name = "ligaoren";

    var expectedStudent = new Likeness<Student, Student>(st1);

    Assert.AreEqual(expectedStudent, st2);
}

This doesn't require you to override Equals on Student.

Likeness performs a semantic comparison, so it can also compare two different types as long as they are semantically similar.