Rename hill-cipher test directory to __test__ for consistency

[Bojun-Vvibe]

Repo: trekhleb/javascript-algorithms (⭐ 195863)
Type: refactor
Files changed: 1
Lines: +0/-0 (file rename only)

What

Renames src/algorithms/cryptography/hill-cipher/_test_ to src/algorithms/cryptography/hill-cipher/__test__. Every other algorithm and data-structure module in this repository uses the double-underscore __test__ naming convention (verified via find src -type d -name "_test_*" — hill-cipher is the lone outlier).

Why

The repo's jest.config.js uses testRegex: '(/__tests__/.*|(\\.|/)(test|spec))\\.jsx?$', so tests are found by filename suffix rather than by directory name. That hides the inconsistency at runtime, but the single-underscore directory name is still a typo that breaks the convention used everywhere else in src/. Aligning it makes the project structure uniform and removes a source of confusion for new contributors looking for tests.

Testing

• git mv preserves file history (verified by git status showing the change as a rename).
• No source code changes — the test file is unchanged and Jest still discovers it via the *.test.js suffix.
• Manual verification: find src -type d -name "_test_" returns no results after the change; __test__ is now the universal convention.

Risk

Low — pure directory rename, no code changes, Jest's testRegex matches by file suffix not directory.