public void provide_value_throws_if_format_string_is_null()
        {
            var converterExtension = new FormatConverterExtension();
            var ex = Assert.Throws <InvalidOperationException>(() => converterExtension.ProvideValue(null));

            Assert.Equal("No format string has been provided.", ex.Message);
        }
        public void provide_value_returns_appropriate_format_converter()
        {
            var converterExtension = new FormatConverterExtension
            {
                FormatString = "format"
            };
            var formatConverter = converterExtension.ProvideValue(null) as FormatConverter;

            Assert.NotNull(formatConverter);
            Assert.Equal("format", formatConverter.FormatString);
        }