public void Given991781544_ReturnEmptyString() { var completeOrgNum = @"991781544"; var orgNumWithouthChecksum = completeOrgNum.Substring(0, completeOrgNum.Length - 1); var generator = new ChecksumGenerator(); var checksum = generator.GenerateChecksum(orgNumWithouthChecksum); var result = generator.ValidateChecksum(completeOrgNum, checksum); result.Should().Be(""); }