fix(runtime) support snapshot testing (#38)

* Support snapshot testing by mocking code when process.mainModule is undefined
* Add babel as dev dependency for unit tests

Author: sam-goodwin

examples/package-lock.json

@@ -7,7 +7,8 @@
   "scripts": {
     "build": "tsc",
     "watch": "tsc -w",
-    "cdk": "cdk"
+    "cdk": "cdk",
+    "test": "jest"
   },
   "dependencies": {
     "@aws-cdk/aws-dynamodb": "^1.4.0",
@@ -28,7 +29,9 @@
     "aws-sdk": "^2.395.0",
     "jest": "^23.6.0",
     "typescript": "^3.4.0",
-    "tslint": "^5.10.0"
+    "tslint": "^5.10.0",
+    "@babel/core": "^7.4.5",
+    "babel-core": "^7.0.0-bridge.0"
   },
   "jest": {
     "testMatch": [