当对象是方法中的参数时，如何正确使用Moq对象

Question

I am not completely new to unit testing, however I am new to the Moq library and I have run into a problem. I am confused on why my unit test fails. Here is the unit test I am trying to write.

[TestInitialize]
    public void SetUp()
    {
        //...
        optionsMock = new Mock<IDictionary<string, string>>();
        //...
    }

[TestMethod]
    public void TestFunction()
    {
        // Arrange
        //var options = new Dictionary<string, string>() { { keyValue, true.ToString() } }; // only way to get the unit test to pass right now
        optionsMock.Setup(a => a.ContainsKey(It.Is<string>(b => b == keyValue))).Returns(false);
        optionsMock.Setup(c => c.Add(It.Is<string>(d => d == keyValue), It.Is<string>(e => e == true.ToString()))).Verifiable();
        optionsMock.Setup(f => f.ContainsKey(It.Is<string>(g => g == keyValue))).Returns(true);
        optionsMock.Setup(h => h[It.Is<string>(i => i == keyValue)]).Returns(true.ToString()); 

        // Act
        int projectId = sut.Open(stringValue, booleanValue, stringValue, stringValue, IDictionary<string, string>, out errorString);

        // Assert
        optionsMock.Verify(a => a.ContainsKey(It.Is<string>(b => b == keyValue)), Times.Once());
        optionsMock.Verify(c => c.Add(It.Is<string>(d => d == keyValue), It.Is<string>(e => e == true.ToString())), Times.Once());
        optionsMock.Verify(f => f.ContainsKey(It.Is<string>(g => g == keyValue)), Times.Once());
        optionsMock.Verify(h => h[It.Is<string>(i => i == keyValue)], Times.Once()); // This fails 
        Assert.AreNotEqual(0, id); // This fails even if I remove the line above
    }

The line commented out is the only way I can get the test to pass, but I feel I should be able to use a mock dictionary as well. The problem I am experiencing is that eventually sut.Open(...) makes a call to an internal class that has an IDictionary as a parameter. In that method there is a check to see if the dictionary is null. Whenever I run the unit test without a real dictionary, the null check always evaluates to true and I get a false fail. However if the real dictionary is passed in, I get a passing test. Here is an example of the internal code.

public int Open(..., IDictionary<string, string> dictionary, ...)
    {
        //...
        if(!dictionary.ContainsKey(key))
        {
           dictionary.Add(key, true);
        }

        InternalClass.Method(dictionary);
        //...
    }

Here is the internal classes method

public void Method(IDictionary<string, string> dictionary)
    {
       if(dictionary != null && dictionary.ContainsKey(key))
       {
          string value = dictionary[key];
          //... Do something
       }
       else
       {
          //... Do something else
       }
    }

It always executes Do something else, is there away around this?

Answer 1

Look closer to the following line:

optionsMock.Setup(a => a.ContainsKey(It.Is<string>(b => b == keyValue))).Returns(false);

This means ContainsKey should return false . So the condition:

if (dictionary != null && dictionary.ContainsKey(key))

can never be satisfied.

I guess you meant to write .Returns(true);

Answer 2

Alright so I think this is the answer I am happy with. I found some other places online where this was used by other people as well. Here is the Setup and Verify section now

bool firstCall = true;

        optionsMock.Setup(a => a.ContainsKey(It.Is<string>(b => b == keyValue))).Returns(() =>
        {
            if (firstCall)
            {
                firstCall = false;
                return false;
            }

            return true;
        });

Then I verify below with the following:

optionsMock.Verify(a => a.ContainsKey(It.Is<string>(b => b == fullPath)), Times.Exactly(2));

The only thing I don't like about this, is the added logic in the test :(. However I don't see any other way around it. Thanks for all the help!