add: unit and integration testing

app/node_modules/exit-x/lib/exit.d.ts

@@ -0,0 +1,8 @@
+/// <reference types="node" />
+
+/**
+ * A replacement for process.exit that ensures stdio are fully drained before exiting.
+ */
+declare function exit(code: number, streams?: [NodeJS.WritableStream, NodeJS.WritableStream]): void;
+
+export = exit;