How do I use Moq and DbFunctions in unit tests to prevent a NotSupportedException?

I know I’m late to the game, but a very simple fix is to write your own method which uses the DbFunction attribute. Then use that function instead of DbFunctions.TruncateTime.

[DbFunction("Edm", "TruncateTime")]
public static DateTime? TruncateTime(DateTime? dateValue)
{
    return dateValue?.Date;
}

Using this function will execute the EDM TruncateTime method when used by Linq to Entities and will run the provided code otherwise.