feat: adding basic unit tests and framework for them

jest.config.js

@@ -0,0 +1,23 @@
+export default {
+  preset: 'ts-jest/presets/default-esm',
+  testEnvironment: 'node',
+  extensionsToTreatAsEsm: ['.ts'],
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.js$': '$1',
+  },
+  transform: {
+    '^.+\\.ts$': [
+      'ts-jest',
+      {
+        useESM: true,
+      },
+    ],
+  },
+  testMatch: ['**/__tests__/**/*.test.ts', '**/?(*.)+(spec|test).ts'],
+  collectCoverageFrom: [
+    'src/**/*.ts',
+    '!src/**/*.d.ts',
+    '!src/**/__tests__/**',
+  ],
+  modulePathIgnorePatterns: ['<rootDir>/dist/', '<rootDir>/node_modules/'],
+};