Moq对于不同的IEnumerable参数设置返回相同的结果

Question

I have come across a very strange behavior in moq and I cannot understand whether it's a bug or I am doing something wrong. Here is the example:

List<CustomerDataTransaction> transactions0 = GetTransactionsSomehow();
List<CustomerDataTransaction> transactions1 = GetTransactionsSomehow();

var portfolioTransactions0 = new List<IPortfolioTransaction>();
var portfolioTransactions1 = new List<IPortfolioTransaction>();

m_TransactionMapperMock
    .Setup(m => m.CreatePortfolioTransactions(transactions0))
    .Returns(portfolioTransactions0);

m_TransactionMapperMock
    .Setup(m => m.CreatePortfolioTransactions(transactions1))
    .Returns(portfolioTransactions1);

I have checked that transaction0 is not equal to transactions1, so it's for sure different lists. But the mock returns portfolioTransactions1 twice when called with different parameters (transactions0 and transactions1). I tried to figure out what was wrong, but I did not find any reasons. Then I have added dummy elements to each of the lists and that has fixed it, mock started to return different values as planned. Is this a bug of Mock or I don't get something? As far as I understand the values inside the list should not affect it at all.

PS I don't know if it's important or not but the method accepts IEnumerable<CustomerDataTransaction>

Answer 1

Consider trying:

It.Is<IEnumerable<CustomerDataTransaction>>(t => t == transactions1))

From memory I thought Moq used reference equality

Answer 2

Expanding on NinjaNye's answer, using It.Is satisfies the test is because it ensures that you are looking at the exact instance of the object, not the equality operator.

With your testing framework, if you say Assert.NotEqual and give it two objects, it uses the equality operator and says one empty list equal to the other. Think about being able to compare objectA.Property1 to objectA.Property2. It makes sense that Assert.Equal would look at the values, not the instance of the value.

Xunit provides a method Assert.Same, which will provide the same functionality as Moq's It.Is<>, verifying it is the same instance of the object. I believe that most of the popular testing frameworks today provide similar behavior.