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yt-dlp-ejs includes comprehensive tests that verify YouTube player JavaScript decryption across multiple runtime environments. Tests run against real YouTube player files to ensure compatibility.

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Test Overview

The test suite validates:
  • N-parameter transformations - URL signature decryption
  • Signature solving - Video signature decryption
  • Multiple player variants - main, tcc, tce, es5, es6, tv, phone variants
  • Cross-runtime compatibility - Deno, Bun, and Node.js
Tests use real YouTube player JavaScript files that are downloaded before running the test suite.

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Setting Up the Test Environment

Before running tests, you need to install dependencies and download player files.

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Step 1: Install Dependencies

Choose your runtime and install dependencies: 
deno install --frozen

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Step 2: Download Player Files

Download the YouTube player JavaScript files used for testing: 
deno run src/yt/solver/test/download.ts
With permissions explicitly granted:
deno run \
  --no-prompt \
  --allow-read=src/yt/solver/test/players/ \
  --allow-write=src/yt/solver/test/players/ \
  --allow-net=www.youtube.com \
  --allow-sys=uid \
  src/yt/solver/test/download.ts
The download script:
  • Fetches player files from YouTube (www.youtube.com)
  • Saves them to src/yt/solver/test/players/
  • Downloads all variants needed for the test suite
  • Uses cached files when available
The download process can take several minutes depending on your connection. Player files are cached locally to speed up subsequent runs.

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Running Tests

Once dependencies are installed and player files are downloaded, run the tests: 
deno test
Run with full permissions:
deno test \
  --no-prompt \
  --no-check \
  --allow-read=src/yt/solver/test/players/
Run specific player variant:
deno test --filter="-main-"

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Test Structure

Tests are organized in src/yt/solver/test/: 
src/yt/solver/test/
├── download.ts      # Downloads player JS files
├── tests.ts         # Test definitions and expected outputs
├── utils.ts         # Test utilities and helpers
├── io.ts           # File I/O operations
└── players/        # Downloaded player files (cached)

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Test Definitions

Each test in tests.ts defines:
  • Player ID - 8-character hash identifying the player version
  • Variants - Which player variants to test (main, tcc, tce, es5, es6, tv, tv_es6, phone)
  • N-parameter tests - Input/expected output pairs for URL decryption
  • Signature tests - Input/expected output pairs for signature decryption
{
  player: "3d3ba064",
  n: [
    { input: "ZdZIqFPQK-Ty8wId", expected: "qmtUsIz04xxiNW" },
    { input: "4GMrWHyKI5cEvhDO", expected: "N9gmEX7YhKTSmw" },
  ],
  sig: [
    {
      input: "gN7a-hudCuAuPH6fByOk1_GNXN0yNMHShjZXS2VOgsEItAJz0tipeavEOmNdYN-wUtcEqD3bCXjc0iyKfAyZxCBGgIARwsSdQfJ2CJtt",
      expected: "ttJC2JfQdSswRAIgGBCxZyAfKyi0cjXCb3gqEctUw-NYdNmOEvaepit0zJAtIEsgOV2SXZjhSHMNy0NXNG_1kNyBf6HPuAuCduh-a7O",
    },
  ],
}
Some tests are marked as “Synthetic test” - these use artificially generated test cases for regression testing.

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Player Variants

The test suite validates multiple YouTube player variants:
  • main - Standard player (player_ias.vflset)
  • tcc - Type-checking compiled (player_ias_tcc.vflset)
  • tce - Type-checking enabled (player_ias_tce.vflset)
  • es5 - ES5-compatible player
  • es6 - ES6+ player
  • tv - TV platform player
  • tv_es6 - TV ES6 player
  • phone - Mobile phone player
  • es6_tcc - ES6 with type-checking compiled
  • es6_tce - ES6 with type-checking enabled
Some player versions have issues with certain variants (e.g., “tce causes exception even in browser”). These are tested across other variants for regression testing.

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What Tests Validate

The test suite ensures:
  1. Correct decryption - Player transformations produce expected outputs
  2. Runtime compatibility - Same results across Deno, Bun, and Node.js
  3. Player variant handling - All player types are correctly processed
  4. Regression prevention - Historical player versions continue working

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Parallel Test Execution

For faster execution, you can run tests in parallel: 
# Deno: Run all variants in parallel
xargs -n 1 -P 10 deno test \
  --no-prompt \
  --no-check \
  --allow-read=src/yt/solver/test/players/ \
  --filter <<<"$(printf -- '-%s-\n' main tcc tce es5 es6 tv tv_es6 phone es6_tcc es6_tce)"
This command:
  • Uses xargs with -P 10 for 10 parallel processes
  • Filters tests by variant name
  • Runs each variant test independently

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CI Test Workflow

The GitHub Actions CI runs tests across:
  • Runtimes: Deno (2.0.0+), Bun (1.2.11+), Node (22.18+)
  • Platforms: Ubuntu and Windows (Python tests)
  • Python versions: 3.10, 3.11, 3.12, 3.13, 3.14, PyPy 3.11
The workflow:
  1. Caches player files based on tests.ts hash
  2. Downloads player files once (15 min timeout)
  3. Runs tests in parallel across all runtimes
  4. Validates Python integration

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Troubleshooting

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Missing Player Files

If tests fail with “player file not found”: 
# Re-download player files
rm -rf src/yt/solver/test/players/*.js
<runtime> run src/yt/solver/test/download.ts

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Permission Errors (Deno)

Deno requires explicit permissions. Use: 
deno test --allow-read=src/yt/solver/test/players/

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Test Failures

If tests fail:
  1. Check you’re using the correct runtime version (see requirements above)
  2. Ensure player files are downloaded successfully
  3. Verify dependencies are installed with frozen lockfiles
  4. Check for network issues during player download
Test failures may indicate YouTube player changes. If multiple tests fail, please report an issue with the failing player IDs.

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Python Tests

To run Python-specific tests: 
# Build the package first
python -m pip install -U build
python -m build

# Unpack the wheel
unzip -u dist/yt_dlp_ejs-*.whl "yt_dlp_ejs/*"

# Run Python tests
python -Werror -m unittest
Python tests verify:
  • Package structure and imports
  • JavaScript integration
  • Cross-platform compatibility (Windows/Linux)

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