[R45-T020] Strengthen regression tests for Autokey.encrypt - #60

Description

Documents the protected input-sanitization, autokey-extension, loop-bound, and modulo-26 conditions on Autokey.encrypt(String, String) in src/main/java/com/thealgorithms/ciphers/Autokey.java, adds a mutation-resistant regression test to src/test/java/com/thealgorithms/ciphers/AutokeyTest.java, and adds work/R45-T020/check.py to execute and record the checks. All existing behavior and public interfaces are preserved, with no deliberate mutant left in the final source.

Related Issue

Fixes: #20

Type of Change

• Bug Fix
• New Feature
• UI/UX Improvement
• Performance Improvement
• Tests
• Documentation
• Refactoring / Maintenance
• CI/CD

Changes Made

• Added Javadoc on Autokey.encrypt(String, String) in src/main/java/com/thealgorithms/ciphers/Autokey.java (lines 14–29) documenting the protected conditions (toUpperCase().replaceAll("[^A-Z]", ""), autokey stream extension over 0 <= i < plaintext.length(), and modulo-26 wrap-around). No executable code or public API was modified.
• Added encryptSmallestOrdinaryAndBoundaryInputsDetectMutants() to src/test/java/com/thealgorithms/ciphers/AutokeyTest.java (lines 38–98) with literal expected values and source-line citations:
  • Smallest valid inputs: ("", "A") → "", ("123!", "A") → "", ("A", "B") → "B".
  • Modulo-26 wrap-around boundary: ("Z", "B") → "A".
  • Minimal autokey extension beyond keyword length: ("BC", "D") → "ED".
  • Ordinary lowercase/spaced input: ("attack at dawn", "queen") → "QNXEPKTMDCGN", verifying fresh equivalent input ("ATTACKATDAWN", "QUEEN"), input immutability, and round-trip decrypt.
• Added work/R45-T020/check.py (with evidence files in work/R45-T020/), running mvn test for AutokeyCipherTest, enforcing a nonzero test count, saving comparisons.txt, result.txt, mvn_output.txt, and tool_versions.txt, and exiting non-zero on failure.

Screenshots / Recordings

Not applicable (no UI changes).

Testing

Command: python3 work/R45-T020/check.py
(runs mvn -B test -Dtest=AutokeyCipherTest -Dsurefire.failIfNoSpecifiedTests=false)

Result: tests=3 failures/errors=0 skipped=0 records=6 mvn_exit=0, status=PASS

Mutant checks (tested on temporary copies and reverted):

• Missing .toUpperCase() on plaintext (line 16 before Javadoc): existing tests (autokeyEncryptTest, autokeyDecryptTest) passed, while encryptSmallestOrdinaryAndBoundaryInputsDetectMutants failed on ("attack at dawn", "queen") (status=FAIL, tests=3 failures/errors=1 skipped=0 mvn_exit=1).
• Off-by-one loop bound i < plaintext.length() - 1 (line 24 before Javadoc): failed with status=FAIL (tests=3 failures/errors=2 skipped=0 mvn_exit=1), caught on ("A", "B") ("" vs "B").

Style: mvn -B checkstyle:check reports 0 Checkstyle violations (BUILD SUCCESS).

Tool versions and check records are saved in work/R45-T020/tool_versions.txt and work/R45-T020/comparisons.txt.

Checklist

• I have tested my changes locally.
• I have added or updated tests, if needed.
• I have updated documentation, if needed.
• I have followed the project's coding guidelines.
• I have run the relevant tests and checks.
• I have addressed previous review feedback, if applicable.

Additional Notes

• No deliberate mutant or test-only branch remains in Autokey.java.

• The work/R45-T020/ evidence folder is for coursework review only and should not go into any later upstream PR.

• I have read CONTRIBUTING.md.

• This pull request is all my own work -- I have not plagiarized it.

• All filenames are in PascalCase.

• All functions and variable names follow Java naming conventions.

• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.

• All new algorithms include a corresponding test class that validates their functionality.

• All new code is formatted with clang-format -i --style=file path/to/your/file.java