feat(testing): add testing module [wip]

babel.config.js

@@ -0,0 +1,10 @@
+module.exports = {
+  'presets': [
+    ['@babel/preset-env', {
+      'targets': {
+        'node': 'current',
+      },
+    }],
+    '@babel/preset-typescript',
+  ],
+};

jest.config.ts

@@ -0,0 +1,22 @@
+import type {Config} from '@jest/types';
+
+export default async (): Promise<Config.InitialOptions> => {
+  return {
+    'verbose': true,
+    'clearMocks': true,
+    'collectCoverage': true,
+    'coverageDirectory': 'tests__coverages',
+    'maxConcurrency': 2,
+    'watchPathIgnorePatterns': [
+      './node_modules/',
+      './lib/',
+    ],
+    'testEnvironment': 'node',
+    'testMatch': [
+      '**/tests/**/*.+(ts)',
+    ],
+    'transform': {
+      '^.+\\.(ts)$': 'ts-jest',
+    },
+  };
+};

package.json

@@ -9,12 +9,19 @@
     "ow": "^0.28.1"
   },
   "devDependencies": {
+    "@babel/core": "^7.16.0",
+    "@babel/preset-env": "^7.16.0",
+    "@babel/preset-typescript": "^7.16.0",
     "@types/ioredis": "^4.28.1",
+    "@types/jest": "^27.0.2",
     "@typescript-eslint/eslint-plugin": "^5.3.0",
     "@typescript-eslint/parser": "^5.3.0",
     "@vercel/node": "^1.12.1",
+    "babel-jest": "^27.3.1",
     "eslint": "^8.2.0",
     "eslint-config-google": "^0.14.0",
+    "jest": "^27.3.1",
+    "ts-node": "^10.4.0",
     "typescript": "^4.4.4"
   },
   "scripts": {