Unit test for Expression tree in c#

Question

How do I write a unit test for a Expression tree in C#.

I have this class which needs to be tested. This method returns a Expression tree and also gets one as a parameter.

code:

public ExpressionStarter<SpecFinderDataModel> DoSearch(bool status, string searchValue, ExpressionStarter<SpecFinderDataModel> predicate)
{
    var localPredicate = predicate;
    if (status == false)
    {
        var searchTerms = searchValue.Split(' ').ToList().ConvertAll(x => x.ToLower());
        localPredicate = localPredicate.Or(s => searchTerms.Any(srch => s.ProductID.ToLower().Contains(srch)));
        localPredicate = localPredicate.Or(s => searchTerms.Any(srch => s.ISBN13.ToLower().Contains(srch)));
        localPredicate = localPredicate.Or(s => searchTerms.Any(srch => s.Title.ToLower().Contains(srch)));
    }
    return localPredicate;
}

Any advice would be helpful. Thanks.

Update #1 I have used LinqKit for ExpressionStarter

Answer 1

This shall be simple, though I will use the Expression<Func<SpecFinderDataModel,bool>> instead of LinqKit APIs, which is used internally, In the DoSearch method, you need Expression<Func<SpecFinderDataModel,bool>> as input, based on the method assuming following as the definition of the type SpecFinderDataModel

public class SpecFinderDataModel
{
    public string ProductID {get; set;}

    public string ISBN13 {get; set;}

    public string Title {get; set;}
}

Now you need to simply test various options, as done in regular unit test, a sample:

   // Initial Expression value constant false is the result
   Expression<Func<SpecFinderDataModel, bool>> expr = c => false;

    // SpecFinderDataModel Object
    var sfd = new SpecFinderDataModel
    {
     ISBN13 = "",
     ProductID = "Test A B C",
     Title = ""
    }

    // Call DoSearch and supply the sfd for testing
    var result = DoSearch(false,"Test",expr).Compile()(sfd);

    // Assert the result in the unit test to understand 
    Assert.True(result,true);

Like this based on combinations of the DoSearch parameters and test object sfd, you can create any number of unit test cases to test your code