spec: initial spike of main-process based tests

spec-main/events-helpers.ts

@@ -0,0 +1,40 @@
+import { EventEmitter } from "electron";
+
+/**
+ * @fileoverview A set of helper functions to make it easier to work
+ * with events in async/await manner.
+ */
+
+/**
+ * @param {!EventTarget} target
+ * @param {string} eventName
+ * @return {!Promise<!Event>}
+ */
+export const waitForEvent = (target: EventTarget, eventName: string) => {
+  return new Promise(resolve => {
+    target.addEventListener(eventName, resolve, { once: true })
+  })
+}
+
+/**
+ * @param {!EventEmitter} emitter
+ * @param {string} eventName
+ * @return {!Promise<!Array>} With Event as the first item.
+ */
+export const emittedOnce = (emitter: EventEmitter, eventName: string) => {
+  return emittedNTimes(emitter, eventName, 1).then(([result]) => result)
+}
+
+export const emittedNTimes = (emitter: EventEmitter, eventName: string, times: number) => {
+  const events: any[][] = []
+  return new Promise<any[][]>(resolve => {
+    const handler = (...args: any[]) => {
+      events.push(args)
+      if (events.length === times) {
+        emitter.removeListener(eventName, handler)
+        resolve(events)
+      }
+    }
+    emitter.on(eventName, handler)
+  })
+}