NSubstitute not matching Linq Expression - linq

Question

I am implementing a repository pattern Query class and testing using NSubstitute.
Repository interface:
public interface IMyRepository
{
IQueryable<T> Query<T>(Expression<Func<T, bool>> filter) where T : class;
}
DateTimeProvider interface:
public interface IMyDateTimeProvider
{
DateTime GetDateNow();
}
Application interface:
public interface IMyApplication
{
List<Thing> GetThingsByQuery(int status);
}
Application implementation:
public class MyApplication : IMyApplication
{
private readonly IMyRepository myRepository;
private readonly IMyDateTimeProvider myDateTimeProvider;
public MyApplication(IMyRepository myRepository, IMyDateTimeProvider myDateTimeProvider)
{
this.myRepository = myRepository;
this.myDateTimeProvider = myDateTimeProvider;
}
public List<Thing> GetThingsByQuery(int status)
{
var createdDate = this.myDateTimeProvider.GetDateNow();
return this.myRepository.Query<Thing>(t => t.CreatedDate == createdDate && t.Status == status).ToList();
}
}
Test:
[TestClass]
public class ApplicationTest
{
private IMyApplication myApplication;
private IMyDateTimeProvider myDateTimeProvider;
private IMyRepository myRepository;
[TestMethod]
public void QueriesRepository()
{
// Arrange
var createdDate = new DateTime(2014, 1, 1);
this.myDateTimeProvider.GetDateNow().Returns(createdDate);
const int Status = 1;
// Act
this.myApplication.GetThingsByQuery(Status);
// Assert
this.myRepository.Received().Query<Thing>(t => t.CreatedDate == createdDate && t.Status == Status);
}
[TestInitialize]
public void TestInitialize()
{
this.myRepository = Substitute.For<IMyRepository>();
this.myDateTimeProvider = Substitute.For<IMyDateTimeProvider>();
this.myApplication = new MyApplication(this.myRepository, this.myDateTimeProvider);
}
}
But the test fails with the following message:
NSubstitute.Exceptions.ReceivedCallsException: Expected to receive a call matching:
Query<Thing>(t => ((t.CreatedDate == value(MySolution.Test.ApplicationTest+<>c__DisplayClass0).createdDate) AndAlso (t.Status == 1)))
Actually received no matching calls.
Received 1 non-matching call (non-matching arguments indicated with '*' characters):
Query<Thing>(*t => ((t.CreatedDate == value(MySolution.Application.MyApplication+<>c__DisplayClass0).createdDate) AndAlso (t.Status == value(MySolution.Application.MyApplication+<>c__DisplayClass0).status))*)
The DateTime and Status are being parsed into value() which are different between the Application and the Test.
Why is this? How can I fix this?

Answer 1

For complicate expressions if often find it easier to assert on captured arguments by using callbacks than with Received(). An (incomplete) example:
Expression<Func<Thing, bool>> receivedFilter receivedFilter = null;
myRepository.When(x => x.Query<Thing>(Arg.Any<...>))
.Do(x => receivedQuery = x.Arg<Expression<Func<Thing, bool>>>());
Then, assert on the captured filter expression. It might actually simpler to just execute the expression's filter func (see e.g. here)
Func<Thing, bool> predicate = receivedFilter.Compile();
var matchingThing = new Thing
{ CreatedDate = createdData, Status = Status };
// assert matching
predicate(matchingThing).Should().BeTrue();
// assert non.matching
predicate(nonMatchingThing).Should().BeFalse();
This approach seems to make the test a little more black-boxed but this is in general not a bad thing.

Answer 2

The default equality comparer for an Expression is being used (referential equality):
eg, the expression (t => t.CreatedDate == createdDate && t.Status == Status``) in:
this.myRepository.Received().Query<Thing>(t => t.CreatedDate == createdDate
&& t.Status == Status );
Is a different instance to the expression in:
return this.myRepository.Query<Thing>(t => t.CreatedDate == createdDate
&& t.Status == status ).ToList();
To fix validate this method call check out argument matchers within NSubstitute.
But as an example:
Func<Expression<Thing, bool>, bool> validator =
// TODO this needs to be written properly, based on the expression,
// not its string representation
e => e.Body.ToString() == "t.CreatedDate == createdDate
&& t.Status == Status";
this.myRepository.Received().Query<Thing>(Arg.Is<Expression<Thing, bool>>(validator));