Add test suite, cover existing functions

package.json

@@ -20,7 +20,9 @@
   "scripts": {
     "build": "rimraf dist && tsc",
     "doc": "typedoc",
-    "test": "echo \"Error: no test specified\" && exit 1",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "preversion": "pnpm test",
     "version": "pnpm run build && pnpm run doc && git add dist docs README.md"
   },
   "author": "Râu Cao <raucao@kosmos.org>",
@@ -31,7 +33,8 @@
     "rimraf": "^6.1.2",
     "typedoc": "^0.28.16",
     "typedoc-plugin-markdown": "^4.9.0",
-    "typescript": "^5.9.3"
+    "typescript": "^5.9.3",
+    "vitest": "^4.0.18"
   },
   "dependencies": {
     "latlon-geohash": "^2.0.0",