private void CheckInvalidTryParse(string input)
        {
            EntityTagHeaderValue result = null;

            Assert.False(EntityTagHeaderValue.TryParse(input, out result));
            Assert.Null(result);
        }
        private void CheckValidTryParse(string input, EntityTagHeaderValue expectedResult)
        {
            EntityTagHeaderValue result = null;

            Assert.True(EntityTagHeaderValue.TryParse(input, out result));
            Assert.Equal(expectedResult, result);
        }