Question

Alright, let’s assume I have a class like the following …

public class Foo : IFoo
{
    public string Bar
    {
        get { ... }
    }

    public void Initialize()
    {
        ...
    }
}

… and as you can see it implements an interface so I can mock it. Now, in my unit test I’m building the mock like this …

var mock = new Mock<IFoo>();
mock.SetupProperty(p => p.Bar).SetReturnsDefault("Some static value here.");

… however, when the test runs I get the following error …

System.ArgumentException: Property IFoo.Bar is read-only.
Parameter name: expression

So, three questions:

1. What am I doing wrong?
2. What do I need to do?
3. Can you please explain how I misunderstood SetReturnsDefault?

Thanks all!

Answer 1

Obviously, the error message is telling you that you can’t mock the read-only property like that. Instead, try:

mock.SetupGet(p => p.Bar).Returns("whatever");

If you want ALL string properties which are not explicitly set up to return some string then do this:

mock.SetReturnsDefault<string>("whatever"); 
// IMPORTANT: don't call mock.SetupGet(p => p.Bar) as it will override default setting