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Testing Rail Fence Cipher Cryptographic Implementation in javascript-algorithms

This test suite validates the Rail Fence Cipher implementation, a classical cryptographic technique, in JavaScript. The tests comprehensively verify both encoding and decoding functionality across different rail counts (bases), ensuring the algorithm correctly transposes characters in the expected zigzag pattern.

Test Coverage Overview

The test suite provides thorough coverage of the Rail Fence Cipher’s core functionality:

Encoding and decoding with base=3 configuration
Encoding and decoding with base=4 configuration
Empty string handling
Various input types including alphanumeric, special characters, and spaces

Implementation Analysis

The testing approach utilizes Jest’s describe/it pattern for structured test organization. Each test case validates both the encoding and decoding functions separately, ensuring bidirectional transformation integrity. The implementation leverages Jest’s expect().toBe() assertions for precise string comparison.

Technical Details

Testing stack includes:

Jest as the primary testing framework
Individual test blocks for encode/decode operations
String-based assertions for cryptographic validation
Modular import structure for cipher functions

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Symmetric testing of encode/decode pairs
Edge case handling with empty strings
Clear test case organization by base value
Descriptive test names that clearly indicate functionality

trekhleb/javascript-algorithms

src/algorithms/cryptography/rail-fence-cipher/__test__/railFenceCipher.test.js

            
import { encodeRailFenceCipher, decodeRailFenceCipher } from '../railFenceCipher';

describe('railFenceCipher', () => {
  it('encodes a string correctly for base=3', () => {
    expect(encodeRailFenceCipher('', 3)).toBe('');
    expect(encodeRailFenceCipher('12345', 3)).toBe(
      '15243',
    );
    expect(encodeRailFenceCipher('WEAREDISCOVEREDFLEEATONCE', 3)).toBe(
      'WECRLTEERDSOEEFEAOCAIVDEN',
    );
    expect(encodeRailFenceCipher('Hello, World!', 3)).toBe(
      'Hoo!el,Wrdl l',
    );
  });

  it('decodes a string correctly for base=3', () => {
    expect(decodeRailFenceCipher('', 3)).toBe('');
    expect(decodeRailFenceCipher('WECRLTEERDSOEEFEAOCAIVDEN', 3)).toBe(
      'WEAREDISCOVEREDFLEEATONCE',
    );
    expect(decodeRailFenceCipher('Hoo!el,Wrdl l', 3)).toBe(
      'Hello, World!',
    );
    expect(decodeRailFenceCipher('15243', 3)).toBe(
      '12345',
    );
  });

  it('encodes a string correctly for base=4', () => {
    expect(encodeRailFenceCipher('', 4)).toBe('');
    expect(encodeRailFenceCipher('THEYAREATTACKINGFROMTHENORTH', 4)).toBe(
      'TEKOOHRACIRMNREATANFTETYTGHH',
    );
  });

  it('decodes a string correctly for base=4', () => {
    expect(decodeRailFenceCipher('', 4)).toBe('');
    expect(decodeRailFenceCipher('TEKOOHRACIRMNREATANFTETYTGHH', 4)).toBe(
      'THEYAREATTACKINGFROMTHENORTH',
    );
  });
});