CODEWITHSUNDEEP
c#moq
epzee
epzee

Reputation: 568

How to mock a ReadOnlyCollection<T> property using moq

I'm trying to mock this ReadOnlyCollection property:

private readonly IList<MyClass> myList = new List<MyClass>();
public virtual ReadOnlyCollection<MyClass> MyList
{
   get
   {
       return new ReadOnlyCollectionBuilder<MyClass>(this.myList).ToReadOnlyCollection();
   }
}

using this mock (as seen here):

IList<MyClass> mockList = GetElements();
mockObj.SetupGet<IEnumerable<MyClass>>(o => o.myList).Returns(mockList);

However at runtime I get an InvalidCastException:

Unable to cast object of type 'System.Collections.Generic.List`1[MyClass]' to
type 'System.Collections.ObjectModel.ReadOnlyCollection`1[MyClass]'.

What am I doing wrong?

Upvotes: 2

Views: 4670

Answers (3)

Spevy
Spevy

Reputation: 1325

A little late, but I think this can be a little less code.

mockObj.SetupGet(o => o.MyList).Returns(GetElements().AsReadOnly);

Upvotes: 0

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236248

Suppose your code really looks like (otherwise it will not compile):

// Arrange
IList<MyClass> stakeHoldersList= GetElements();
mockObj.SetupGet<IEnumerable<MyClass>>(o => o.MyList).Returns(stakeHoldersList);
// Act on SUT which uses mockObj

You have property MyList of type ReadOnlyCollection<MyClass> but you are trying to return IEnumerable<MyClass>. Thats why you get that error. So, change:

ReadOnlyCollection<MyClass> stakeHoldersList = new ReadOnlyCollection<MyClass>(GetElements());
mockObj.SetupGet<ReadOnlyCollection<MyClass>>(o => o.MyList).Returns(stakeHoldersList);

To avoid such runtime errors, do not specify type of SetupGet method. In this case return value type will inferred from property type and you will get error immediately (code won't compile if return value type does not match property type):

mockObj.SetupGet(o => o.MyList).Returns(stakeHoldersList);

Upvotes: 2

Trevor Pilley
Trevor Pilley

Reputation: 16403

You can't mock the private readonly property myList, what you can do is override the public property MyList since it is marked virtual. In order to do that, you need to update this code:

IList<MyClass> mockList = GetElements();
mockObj.SetupGet<IEnumerable<MyClass>>(o => o.myList).Returns(mockList);

to this:

var mockList = new ReadOnlyCollection<MyClass>(GetElements());
mockObj.Setup(o => o.MyList).Returns(mockList);

Upvotes: 1

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