How to Moq Setting an Indexed property

c#, moq

Solution

This should work

[Test]
public void MoqUsingSetup()
{
    //arrange
    var index = new Mock();
    index.SetupSet(o => o["Key"] = "Value").Verifiable();
    // act
    index.Object["Key"] = "Value";
    //assert
    index.Verify();
}

You can just treat it like a normal property setter.

Problem

I'm trying to use mock to verify that an index property has been set. Here's a moq-able object with an index: ``` public class Index { IDictionary<object ,object> _backingField = new Dictionary<object, object>(); public virtual object this[object key] { get { return _backingField[key]; } set { _backingField[key] = value; } } } ``` First, tried using `Setup()`: ``` [Test] public void MoqUsingSetup() { //arrange var index = new Mock<Index>(); index.Setup(o => o["Key"]).Verifiable(); // act index.Object["Key"] = "Value"; //assert index.Verify(); } ``` ...which fails - it must be verifying against `get{}` So, I tried using `SetupSet()`: ``` [Test] public void MoqUsingSetupSet() { //arrange var index = new Mock<Index>(); index.SetupSet(o => o["Key"]).Verifiable(); } ``` ... which gives a runtime exception: ``` System.ArgumentException : Expression is not a property access: o => o["Key"] at Moq.ExpressionExtensions.ToPropertyInfo(LambdaExpression expression) at Moq.Mock.SetupSet(Mock mock, Expression`1 expression) at Moq.MockExtensions.SetupSet(Mock`1 mock, Expression`1 expression) ``` What's the correct way to accomplish this?

Original source