private void CheckInvalidParsedValue(string input, int startIndex)
        {
            DateHeaderParser parser = DateHeaderParser.Parser;
            object           result = null;
            int newIndex            = startIndex;

            Assert.False(parser.TryParseValue(input, null, ref newIndex, out result));
            Assert.Null(result);
            Assert.Equal(startIndex, newIndex);
        }
        private void CheckValidParsedValue(string input, int startIndex, DateTimeOffset expectedResult,
                                           int expectedIndex)
        {
            DateHeaderParser parser = DateHeaderParser.Parser;
            object           result = null;

            Assert.True(parser.TryParseValue(input, null, ref startIndex, out result));
            Assert.Equal(expectedIndex, startIndex);
            Assert.Equal(expectedResult, result);
        }