public void GetOnlyNumber_NullLine_ArgumentNullException()
        {
            // Arrange
            string line = null;

            // Act and Assert
            Assert.Throws <ArgumentNullException>(() => Parser.GetOnlyNumber(line));
        }
        public void GetOnlyNumber_IncorrectLine_InvalidInputStringException()
        {
            // Arrange
            string line = string.Empty;

            // Act and Assert
            Assert.Throws <InvalidInputStringException>(() =>
            {
                Parser.GetOnlyNumber(line);
            });
        }