.net core - Need help mocking interface

Question

I have the following method to test:

public static DateTime? GetLastSourceUpdateDate(this IQueryableDataFacade facade, long idDevice, long idMeasureType)
        {
            return facade.ExecuteExpression<SynchonizerLastUpdate, DateTime?>(logs =>
            {
                return logs.Where(log => log.IdDeviceMeasureType == idMeasureType && log.Device.Id == idDevice).Select(r => r.LastUpdateDate).FirstOrDefault();
            });
        }

So, I need to mock the interface IQueryableDataFacade for this. I have tried:

[Fact]
        public void ItReturnsNullWhenNoValueIsPresentForThatEntity()
        {
            List<SynchonizerLastUpdate> datasource = new List<SynchonizerLastUpdate>() { 
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 1}, IdDeviceMeasureType = 1, LastUpdateDate = new DateTime(2020, 1, 1) },
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 1}, IdDeviceMeasureType = 1, LastUpdateDate = new DateTime(2020, 1, 1) },
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 1}, IdDeviceMeasureType = 1, LastUpdateDate = new DateTime(2020, 1, 1) }};

            var facadeService = new Mock<IQueryableDataFacade>();
            facadeService.Setup(m => m.ExecuteExpression<SynchonizerLastUpdate, DateTime?>(It.IsAny<Func<IQueryable<SynchonizerLastUpdate>, DateTime?>>())).Returns((p) => { datasource.Select(p)});
        }

But it's not compiling, there's an error on the return type of the mocked method. It says a semicolon is missing, but if I add it, it brokes again, and I'm having troubles to fix it.

question from:https://stackoverflow.com/questions/65944758/need-help-mocking-interface

Answer 1

Ok, I found the solution, I was following a wrong approach. I need to execute the function parameter p, giving it as parameter the IQueryable

[Fact]
        public void ItReturnsRightDateFromDataSource()
        {
            List<SynchonizerLastUpdate> datasource = new List<SynchonizerLastUpdate>() { 
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 1}, IdDeviceMeasureType = 1, LastUpdateDate = new DateTime(2020, 1, 1) },
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 2}, IdDeviceMeasureType = 2, LastUpdateDate = new DateTime(2020, 1, 2) },
                new SynchonizerLastUpdate() { Id = 1, Device = new Device() { Id = 3}, IdDeviceMeasureType = 3, LastUpdateDate = new DateTime(2020, 1, 3) }};

            var facadeService = new Mock<IQueryableDataFacade>();
            facadeService.Setup(m => m.ExecuteExpression(It.IsAny<Func<IQueryable<SynchonizerLastUpdate>, DateTime?>>())).Returns((Func<IQueryable<SynchonizerLastUpdate>, DateTime?> p) => 
            {
                IQueryable<SynchonizerLastUpdate> queryable = datasource.AsQueryable();
                return p(queryable);
            });

            var result = facadeService.Object.GetLastSourceUpdateDate(2, 2);
            Assert.Equal(new DateTime(2020, 1, 2), result);
        }