public void ToJsonString_Test()
        {
            // Arrange
            var obj1 = int.MaxValue;

            Debug.WriteLine($"obj1 - {obj1.ToJsonString()}");

            var obj2 = new DateTime(200, 12, 21);

            Debug.WriteLine($"obj1 - {obj2.ToJsonString()}");

            var obj3 = new ReferenceData {
                Code = "xyz", Description = "123"
            };

            Debug.WriteLine($"obj3 - {obj3.ToJsonString()}");

            IEnumerable <IReferenceData> obj4 = new List <IReferenceData> {
                new SqlReferenceDataSource(), new ApiReferenceDataSource()
            };

            Debug.WriteLine($"obj4 - {obj4.ToJsonString()}");

            // Act

            // Assert
        }