Testing a method with dynamic LINQ queries in C# - Unexpected null reference during unit testing
I'm migrating some code and I'm relatively new to this, so bear with me. Quick question that's been bugging me - I'm working with a `NullReferenceException` when attempting to test a method that constructs a dynamic LINQ query. The method is designed to filter a collection based on a set of criteria. Here is the code for the method I'm trying to test: ```csharp public List<MyEntity> FilterEntities(IEnumerable<MyEntity> entities, string criteria) { if (entities == null) throw new ArgumentNullException(nameof(entities)); if (string.IsNullOrWhiteSpace(criteria)) throw new ArgumentException("Criteria want to be null or empty", nameof(criteria)); var result = entities.AsQueryable().Where(criteria).ToList(); return result; } ``` In my unit test, I'm using Moq to create a mock list of `MyEntity`, but I'm running into issues when passing the criteria. Here’s how my unit test looks: ```csharp [Test] public void FilterEntities_ShouldReturnFilteredResults_WhenValidCriteriaProvided() { var mockData = new List<MyEntity> { new MyEntity { Id = 1, Name = "Alice" }, new MyEntity { Id = 2, Name = "Bob" }, new MyEntity { Id = 3, Name = "Charlie" } }.AsQueryable(); var criteria = "Name.Contains(\"A\")"; var result = FilterEntities(mockData, criteria); Assert.IsNotNull(result); Assert.AreEqual(2, result.Count); } ``` However, when I run this test, it throws a `NullReferenceException` pointing to the line where `Where(criteria)` is called. I've verified that `mockData` is not null. I suspect the scenario may be related to how the `criteria` string is being processed dynamically. I've also tried using `System.Linq.Dynamic.Core` to parse the criteria, but that didn’t help either. Can anyone provide guidance on how to properly set this up for unit testing, or is there a better approach to dynamically filtering with LINQ in unit tests? I'm using .NET 5.0 and NUnit 3.13.2. This is part of a larger web app I'm building. What am I doing wrong? My development environment is Linux. Has anyone else encountered this? I recently upgraded to C# stable. Any advice would be much appreciated.