public string TrimStartOnce(string input, string startsWith)
{
string result = CommonStringExtensions.TrimStartOnce(input, startsWith);
PexAssert.IsNotNull(result);
PexAssert.IsTrue(result.Length <= input.Length);
int originalStartsWithCount = CommonStringExtensions.CountSubstringStart(input, startsWith);
int resultStartsWithCount = CommonStringExtensions.CountSubstringStart(result, startsWith);
PexAssert.IsTrue(originalStartsWithCount - resultStartsWithCount <= 1);
return(result);
}