How to MOQ an Indexed property

Question

I am attempting to mock a call to an indexed property. I.e. I would like to moq the following:

object result = myDictionaryCollection["SomeKeyValue"];

and also the setter value

myDictionaryCollection["SomeKeyValue"] = myNewValue;

I am doing this because I need to mock the functionality of a class my app uses.

Does anyone know how to do this with MOQ? I've tried variations on the following:

Dictionary<string, object> MyContainer = new Dictionary<string, object>();
mock.ExpectGet<object>( p => p[It.IsAny<string>()]).Returns(MyContainer[(string s)]);

But that doesn't compile.

Is what I am trying to achieve possible with MOQ, does anyone have any examples of how I can do this?

Wouldn't it be easier to just use a stub object? Set the required values and check the indexes you need. — Søren Spelling Lund, Dec 05 '08 at 08:23

score 125 · Answer 1 · edited Mar 08 '16 at 14:19

125

It's not clear what you're trying to do because you don't show the declaration of the mock. Are you trying to mock a dictionary?

MyContainer[(string s)] isn't valid C#.

This compiles:

var mock = new Mock<IDictionary>();
mock.SetupGet( p => p[It.IsAny<string>()]).Returns("foo");

edited Mar 08 '16 at 14:19

vauhochzett

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answered Dec 11 '08 at 12:06

Mike Scott

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1

this works as well. except the new syntax uses `SetupSet` instead of `ExpectGet`. also works for setters as well. – tmont Jul 02 '10 at 18:31
1

The IDictionary is from System.Collections and not from System.Collections.Generic – upInCloud Aug 05 '16 at 06:38
What if I want to return different values based on keys? – Ahmad Feb 13 '21 at 15:07
@Ahmad then use It.Is() instead of It.IsAny(). See https://stackoverflow.com/questions/9122070/multiple-moq-it-isstring-matching-arguments – Mike Scott Feb 14 '21 at 17:30

score 20 · Answer 2 · edited Oct 18 '18 at 19:21

As you correctly spotted, there are distinct methods SetupGet and SetupSet to initialize getters and setters respectively. Although SetupGet is intended to be used for properties, not indexers, and will not allow you handling key passed to it. To be precise, for indexers SetupGet will call Setup anyway:

internal static MethodCallReturn<T, TProperty> SetupGet<T, TProperty>(Mock<T> mock, Expression<Func<T, TProperty>> expression, Condition condition) where T : class
{
  return PexProtector.Invoke<MethodCallReturn<T, TProperty>>((Func<MethodCallReturn<T, TProperty>>) (() =>
  {
    if (ExpressionExtensions.IsPropertyIndexer((LambdaExpression) expression))
      return Mock.Setup<T, TProperty>(mock, expression, condition);
    ...
  }
  ...
}

To answer your question, here is a code sample using underlying Dictionary to store values:

var dictionary = new Dictionary<string, object>();

var applicationSettingsBaseMock = new Mock<SettingsBase>();
applicationSettingsBaseMock
    .Setup(sb => sb[It.IsAny<string>()])
    .Returns((string key) => dictionary[key]);
applicationSettingsBaseMock
    .SetupSet(sb => sb["Expected Key"] = It.IsAny<object>())
    .Callback((string key, object value) => dictionary[key] = value);

As you can see, you have to explicitly specify key to set up indexer setter. Details are described in another SO question: Moq an indexed property and use the index value in the return/callback

This is what I was looking for!! None of the other examples worked — Fiona - myaccessible.website, Aug 10 '18 at 17:41

score 20 · Answer 3 · answered May 14 '09 at 02:29

Ash, if you want to have HTTP Session mock, then this piece of code does the job:

/// <summary>
/// HTTP session mockup.
/// </summary>
internal sealed class HttpSessionMock : HttpSessionStateBase
{
    private readonly Dictionary<string, object> objects = new Dictionary<string, object>();

    public override object this[string name]
    {
        get { return (objects.ContainsKey(name)) ? objects[name] : null; }
        set { objects[name] = value; }
    }
}

/// <summary>
/// Base class for all controller tests.
/// </summary>
public class ControllerTestSuiteBase : TestSuiteBase
{
    private readonly HttpSessionMock sessionMock = new HttpSessionMock();

    protected readonly Mock<HttpContextBase> Context = new Mock<HttpContextBase>();
    protected readonly Mock<HttpSessionStateBase> Session = new Mock<HttpSessionStateBase>();

    public ControllerTestSuiteBase()
        : base()
    {
        Context.Expect(ctx => ctx.Session).Returns(sessionMock);
    }
}

What part of this code makes the code under test use the mock session? Is `TestSuiteBase` a library or your own class? — StuperUser, Feb 15 '11 at 19:00

score 11 · Answer 4 · edited Jul 22 '15 at 15:29

11

Its not that difficult but it took a little bit to find it :)

var request = new Moq.Mock<HttpRequestBase>();
request.SetupGet(r => r["foo"]).Returns("bar");

edited Jul 22 '15 at 15:29

Brent Worden

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answered May 06 '15 at 20:09

JustEngland

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score 0 · Answer 5 · answered May 29 '23 at 09:15

This question is very old, and no doubt many of these answers were right at the time of writing, but in 2023 (Moq v4.18.3) and presumably for some time now, there is a very easy solution for this.

One can simply use the method-signature setup to achieve this and get access to the variable parameters sent to the method:

var myDict = new Dictionary<string, string> {
    { "quote", "For {0} the bell tolls" }
};

var mockIndexableObj = new Mock<IIndexableObj>();
mockIndexableObj
    .Setup( i => i[It.IsAny<string>(), It.IsAny<string>()] )
    .Returns<string,string>( (arg1, arg2) => string.Format( myDict[arg1], arg2 ) );

Assert.AreEqual( "For whom the bell tolls",  mockIndexableObj.Object["quote", "whom"];

... just in case anyone happens upon this answer in 2023!

score -5 · Accepted Answer · answered Mar 16 '09 at 08:39

It appears that what I was attempting to do with MOQ is not possible.

Essentially I was attempting to MOQ a HTTPSession type object, where the key of the item being set to the index could only be determined at runtime. Access to the indexed property needed to return the value which was previously set. This works for integer based indexes, but string based indexes do not work.

How to MOQ an Indexed property

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