Moq: Lambda expressions as parameters and evaluate them in returns

c#, lambda, moq, unit-testing

Solution

Yes, it is possible. You can pass a function to `Returns` that takes the expression passed to `Find`, compiles the expression into a `Func<ListObject, bool>`, and applies that to your `testList`:

mockUnitOfWork
    .Setup(uow => uow.Find(It.IsAny<Expression<Func<ListObject, bool>>>()))
    .Returns(new Func<Expression<Func<ListObject, bool>>, IQueryable<ListObject>>(
        expr => testList.Where(expr.Compile()).AsQueryable()));

Problem

In my unit tests I want to be able to moq the "find" function of my repository in my Unit of Work that takes in a lambda express. For example: ``` public virtual IQueryable<T> Find(Expression<Func<T, bool>> predicate) { // Find OPS } ``` I created test lists to represent my dbSets in my unit tests (Also I left out a lot of abstraction to make this more simple for this question): ``` [TestMethod] public void FindTest() { var mockUnitOfWork = new Mock<IUnitOfWork>(); var testList = new List<ListObject> { // Test values } // Here is where I am stuck: mockUnitOfWork.Setup(uow => uow.Find(It.IsAny<Expression<Func<ListObject, bool>>>())) .Returns(/* ???? testList.Where(??????) ???? */); } ``` I want to be able to use the lambda passed by the method calling the mock's find to search within my mocked list. Is this possible? EDIT: Thanks to Chris for the answer. This is setup code to pass the lambda expression that is passed by the method that references the mock's function: ``` mockUnitOfWork .Setup(uow => uow.Find(It.IsAny<Expression<Func<ListObject, bool>>>())) .Returns(new Func<Expression<Func<ListObject, bool>>, IQueryable<ListObject>>( expr => testList.Where(expr.Compile()).AsQueryable())); ```

Original source