Using NSubstitute

A good quick guide is provided - Quick Guide

Create a mock for a given inteface:

MockIXXX = Substitute.For<Ixxx>();

The mocked methods always do nothing and return the default value.

Afterwards can mock a return value:

MockIXXX.GetDuplicates().Returns( GetSomeTestResults() ); 

where GetSomeTestResults() is a test method returning the desired results.

A property can be Mocked using standard notation (if it has a getter and a setter)

MockIXXX.Name = "Algol";

When the property is a getter only use the following technique.

MockIXXX.Key.Returns(999);

Do something when a method AddSelection(ISelection) is called with any parameters:

MockIXXX.When( x => x.AddSelection( Arg.Any<ISelection>() ) ).

    Do( arg => dummySelections.Add( arg.Arg<ISelection>() ) );

here dummySelections is a list local to the test.

When testing results: 

// Test 1 call to UpdateView was received on the given MockObject
MockObject.Received(1).UpdateView();
// Test a property was set to a particular value
MockObject.Received().SomeProperty = 10.0d;
// Test no calls to RemovePage were received on the given MockObject with the specified arguments  
MockObject.DidNotReceive().RemovePage( Arg.Any<IControl>() ); 

// Test 1 call to Add() was received on the given MockObject with the given argument
MockObject.Received(1).Add( Arg.Is<INotification>( arg => arg.Id == NotificationEnum.Clean ) ); 
// No calls to Add() were received on the given MockObject with the given argument
MockObject.DidNotReceive().Add( Arg.Is<INotification>( arg => arg.Id == NotificationEnum.Clean ) )
// Test a call was received regardless of the argument value
MockObject.Received( 1 ).Calculate( Arg.Any() );

// When you have multiple tests in a test fixture you sometimes need to clear the received calls
// otherwise the previous tests could have increased the call count
MockObject.ClearReceivedCalls();

Checking calls were received in a particular order:

Received.InOrder(() =>
{
 MockIXxx.SomeMethodCall();
 MockIYyy.AnotherMethodCall(Arg.Any<string>());
});

NSubstitute syntax for raising events is a bit more subtle:

MockObject.SomeEvent += Raise.EventWith(new object(), new EventArgs());

See the NSubstitute documentation here

Random Extension

An extension to the Random class to help convert the random number generator class to generate more than just integers. It is very simple to use, pass your array of random choices as parameters to the method.
Hint: Make your Random instance static so that the choice of random values is not continually reset back to the start.

private static Random random = new Random();
...
/// <summary>
/// An extension to the Random class to help convert the random generator to 
/// generate more than just integers. It is very simple to use, pass your 
/// array of random choices as parameters to the method.
/// </summary>
/// <example>
/// For example, say you want something chosen at random from the following 
/// set of football teams:
/// "Liverpool", "Southampton", "Manchester United", "Barcelona"
/// then use the following line: 
/// string randomTeam = random.NextFromSet<T>("Liverpool", 
///                      "Southampton", "Manchester United", "Barcelona");
/// </example>
public static class RandomExtensions
{
 public static T NextFromSet<T>(this Random random, params T[] set)
 {
  return set[random.Next(0, set.Length)];
 }
}

...
string randomTeam = random.NextFromSet<string>("Liverpool", "Southampton", 
      "Manchester United", "Barcelona");