Fix linter errors; add domain; add unit test support

tsconfig.json

@@ -3,6 +3,7 @@
     "target": "esnext",
     "module": "esnext",
     "strict": true,
+    "strictNullChecks": false,
     "jsx": "preserve",
     "importHelpers": true,
     "moduleResolution": "node",
@@ -34,6 +35,7 @@
     "tests/**/*.tsx"
   ],
   "exclude": [
-    "node_modules"
+    "node_modules",
+    "**/*.spec.ts"
   ]
 }