Need help to understand Moq better

It.IsAny / It.Is

These can be useful when you're passing a new reference type within the code under test. For instance, if you had a method along the lines of:

public void CreatePerson(string name, int age) {
    Person person = new Person(name, age);
    _personRepository.Add(person);
}

You might want to check the add method has been called on the repository,

[Test]
public void Create_Person_Calls_Add_On_Repository () {
    Mock<IPersonRepository> mockRepository = new Mock<IPersonRepository>();
    PersonManager manager = new PersonManager(mockRepository.Object);
    manager.CreatePerson("Bob", 12);
    mockRepository.Verify(p => p.Add(It.IsAny<Person>()));
}

If you wanted to make this test more explicit you can use It.Is by supplying a predicate the person object must match,

[Test]
public void Create_Person_Calls_Add_On_Repository () {
    Mock<IPersonRepository> mockRepository = new Mock<IPersonRepository>();
    PersonManager manager = new PersonManager(mockRepository.Object);
    manager.CreatePerson("Bob", 12);
    mockRepository.Verify(pr => pr.Add(It.Is<Person>(p => p.Age == 12)));
}

This way the test will through an exception if the person object that was used to call the add method didn't have the age property set to 12.

Times

If you had a method along the lines of:-

public void PayPensionContribution(Person person) {
    if (person.Age > 65 || person.Age < 18) return;
    //Do some complex logic
    _pensionService.Pay(500M);
}

One of the things that you might want to test is that the pay method does not get called when a person aged over 65 is passed into the method

[Test]
public void Someone_over_65_does_not_pay_a_pension_contribution() {
    Mock<IPensionService> mockPensionService = new Mock<IPensionService>();
    Person p = new Person("test", 66);
    PensionCalculator calc = new PensionCalculator(mockPensionService.Object);
    calc.PayPensionContribution(p);
    mockPensionService.Verify(ps => ps.Pay(It.IsAny<decimal>()), Times.Never());
}

Similarly, it's possible to imagine situations where you're iterating over a collection and calling a method for each item in the collection and you'd like to make sure that it's been called a certain amount of times, other times you simply don't care.

SetupGet / SetupSet

What you need to be aware of with these guys is that they reflect how your code is interacting with the mock rather than how you're setting up the mock

public static void SetAuditProperties(IAuditable auditable) {
    auditable.ModifiedBy = Thread.CurrentPrincipal.Identity.Name;
}

In this case, the code is setting the ModifiedBy property of the IAuditable instance while it's getting the Name property of the current instance of IPrincipal,

[Test]
public void Accesses_Name_Of_Current_Principal_When_Setting_ModifiedBy() {
    Mock<IPrincipal> mockPrincipal = new Mock<IPrincipal>();
    Mock<IAuditable> mockAuditable = new Mock<IAuditable>();

    mockPrincipal.SetupGet(p => p.Identity.Name).Returns("test");

    Thread.CurrentPrincipal = mockPrincipal.Object;
    AuditManager.SetAuditProperties(mockAuditable.Object);

    mockPrincipal.VerifyGet(p => p.Identity.Name);
    mockAuditable.VerifySet(a => a.ModifiedBy = "test");
}

In this case, we're setting up the name property on the mock of IPrincipal so it returns "test" when the getter is called on the Name property of Identity we're not setting the property itself.

SetupProperty / SetupAllProperties

Looking at the test above if it was changed to read

[Test]
public void Accesses_Name_Of_Current_Principal_When_Setting_ModifiedBy() {
    Mock<IPrincipal> mockPrincipal = new Mock<IPrincipal>();
    Mock<IAuditable> mockAuditable = new Mock<IAuditable>();
    mockPrincipal.SetupGet(p => p.Identity.Name).Returns("test");

    var auditable = mockAuditable.Object;

    Thread.CurrentPrincipal = mockPrincipal.Object;
    AuditManager.SetAuditProperties(auditable);

    Assert.AreEqual("test", auditable.ModifiedBy);
}

The test would fail. This is because the proxy created by Moq doesn't actually do anything in the set method of a property unless you tell it to. In effect, the mock object looks a bit like this

public class AuditableMock : IAuditable {
     public string ModifiedBy { get { return null; } set { } }

} 

To get the test to pass you have to tell Moq to set up the property to have the standard property behavior. You can do this by calling SetupProperty and the mock will look more like

public class AuditableMock : IAuditable {
     public string ModifiedBy { get; set; }
} 

and the test above would pass as the value "test" would now get stored against the mock. When mocking complex objects you might want to do this for all properties, hence the SetupAllProperties shortcut

Finally, the lightbulb in the IDE is the ReSharper plugin.

If you don't care about the exact value of a property, it's far better to use .IsAny because you are being explicit about the fact that the exact value is not important. If you hardcode it as "abc", then it is not clear if your code you are testing depends on starting with "a" or ending with "c" or being 3 chars long, etc. etc.