public void IsValidShouldReturnTrueIfInputIsValidPositiveString(string salaryToTest)
        {
            var salaryValidation = new SalaryValidationService();

            var result = salaryValidation.IsValid(salaryToTest);

            result
            .Should()
            .BeTrue();
        }
        public void IsValidShouldReturnFalseIfInputIsInvalidString(string salaryToTest)
        {
            var salaryValidation = new SalaryValidationService();

            var result = salaryValidation.IsValid(salaryToTest);

            result
            .Should()
            .BeFalse();
        }