Multiple Moq It.Is() Matching Arguments

Isn’t it confusing? You are trying to mock GetUser method but you set the Returns for that function’s return value’s property. You also want to state return type’s property based on mocked method.

Here’s a way a more clear way:

mockMembershipService.Setup(x => x.GetUser(It.IsAny<string>())
                     .Returns<string>(GetMembershipUser);

Here’s a method to create the membership mock:

private MembershipUser GetMembershipUser(string s)
{
    Mock<MembershipUser> user =new Mock<MembershipUser>();
    user.Setup(item => item.ProviderUserKey).Returns(GetProperty(s));
    return user.Object;
}

Then you write a method for setting that property:

private string GetProperty(string s)
{
    if(s.Contains("Joe"))
        return "1234abcd";
    else if(s.Contains("Tracy"))
        return "5678efgh";
}