public void CipherTest_ContainsInvalidTrue()
{
SubstitutionCipher cipher = new SubstitutionCipher();
Assert.That(cipher.ContainsInvalid("Not all valid!"), Is.True);
}
public void CipherTest_ContainsInvalidFalse()
{
SubstitutionCipher cipher = new SubstitutionCipher();
Assert.That(cipher.ContainsInvalid("these are all valid"), Is.False);
}