Fix timing issues in char width test

test/api/TestUtils.ts

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2019 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import * as puppeteer from 'puppeteer';
+
+export async function pollFor<T>(page: puppeteer.Page, evalOrFn: string | (() => Promise<T>), val: T, preFn?: () => Promise<void>): Promise<void> {
+  if (preFn) {
+    await preFn();
+  }
+  const result = typeof evalOrFn === 'string' ? await page.evaluate(evalOrFn) : await evalOrFn();
+  let equal = false;
+  if (typeof result === 'object') {
+    equal = Object.keys(result).every(e => result[e] === (val as any)[e]);
+  } else {
+    equal = result === val;
+  }
+  if (!equal) {
+    return new Promise<void>(r => {
+      setTimeout(() => r(pollFor(page, evalOrFn, val, preFn)), 10);
+    });
+  }
+}