public void ReturnsSourceStringIfNullOrEmptyKey(string source, string key)
        {
            //Arrange
            VigenereEncryptor encryptor = new VigenereEncryptor();

            //Act
            string result = encryptor.EncryptString(source, key);

            //Assert
            Assert.AreEqual(source, result);
        }
        public void ReturnsEmptyStringIfNullOrEmptySource(string source, string key)
        {
            //Arrange
            VigenereEncryptor encryptor = new VigenereEncryptor();

            //Act
            string result = encryptor.EncryptString(source, key);

            //Assert
            Assert.IsEmpty(result);
        }
        public void ReturnsEncryptedStringWhenParamsNotNullOrEmpty(
            string source,
            string key,
            string expectedResult)
        {
            //Arrange
            VigenereEncryptor encryptor = new VigenereEncryptor();

            //Act
            string actualResult = encryptor.EncryptString(source, key);

            //Assert
            Assert.AreEqual(expectedResult, actualResult);
        }