public void ValidateGuidToBeEmpty()
        {
            // Given
            var validator = new GuidValidator(Guid.Empty);

            // When
            validator.BeEmpty();

            // Then
            Assert.True(true);
        }
        public void ValidateGuidToBeEmptyViolated()
        {
            // Given
            var guid      = Guid.NewGuid();
            var validator = new GuidValidator(guid);

            // When
            var exception = Assert.Throws <XunitException>(() => validator.BeEmpty(because: "that's the bottom line"));

            // Then
            Assert.NotNull(exception);
            var rn = Environment.NewLine;

            Assert.Equal(
                $"{rn}validator{rn}is \"{guid}\"{rn}but was expected to be empty{rn}because that's the bottom line",
                exception.UserMessage);
        }