https://stackoverflow.com/q/47873262/906

a.cs

using System;
using System.Collections.Generic;
using System.Linq;
using MongoDB.Bson;
using MongoDB.Driver;
using NSubstitute;
using NSubstitute.ExceptionExtensions;
using Xunit;

namespace NSubWorkshop
{
    public class ComponentRecordDataModel
    {
        public string Id { get; set; }
        public List<string> UserViews { get; set; } = new List<string>();
    }
    public interface IMongoContext {
        IEnumerable<T> Find<T>(FilterDefinition<T> filter, ProjectionDefinition<T> projection);
    }
    public class SampleClass
    {
        IMongoContext MongoContext;
        public SampleClass(IMongoContext context)
        {
            this.MongoContext = context;
        }

        public ComponentRecordDataModel GetRecordUserViews(string id)
        {
            var filter = Builders<ComponentRecordDataModel>.Filter.Eq(x => x.Id, id);
            var projection = Builders<ComponentRecordDataModel>.Projection.Include(x => x.UserViews);
            var result = MongoContext.Find(filter, projection).FirstOrDefault();
            return result;
        }
    }
    public class DataAccessException : Exception {}
    public class MongoTest
    {
        [Fact]
        public void LogsExceptionWhenOnGetRecordUserViews()
        {
            var _exception = new DataAccessException();
            var _recordModel = new ComponentRecordDataModel { Id = "123", UserViews = { "a", "b" } };
            var _mongoContext = Substitute.For<IMongoContext>();
            var _collection = new SampleClass(_mongoContext);

            var filter = Builders<ComponentRecordDataModel>.Filter.Eq(x => x.Id, _recordModel.Id);
            var projection = Builders<ComponentRecordDataModel>.Projection.Include(x => x.UserViews);

            var expectedFilter = Arg.Is<FilterDefinition<ComponentRecordDataModel>>(
                x => ToJson(x).Equals(ToJson(filter)));
            var expectedProjection = Arg.Is<ProjectionDefinition<ComponentRecordDataModel>>(
                x => ToJson(x).Equals(ToJson(projection)));

            _mongoContext.Find(expectedFilter, expectedProjection).Throws(_exception);

            Assert.Throws(typeof(DataAccessException), () => _collection.GetRecordUserViews(_recordModel.Id));
        }

        static string ToJson<T>(T t)
        {
            // Avoiding Error CS0854: An expression tree may not contain a call or invocation that uses optional arguments
            return t.ToJson();
        }
    }
}