public void InvalidListingException_ReturnsDefaultErrorMessage()
        {
            // Act
            var error = new InvalidListingException();

            // Assert
            Assert.Equal("Invalid listing ID", error.Message);
            Assert.Equal(typeof(InvalidListingException), error.GetType());
        }
        public void InvalidListingException_ReturnsProvidedErrorMessage(string errorMessage)
        {
            // Act
            var error = new InvalidListingException(errorMessage);

            // Assert
            Assert.Equal(errorMessage, error.Message);
            Assert.Equal(typeof(InvalidListingException), error.GetType());
        }