Extract millisFromDuration helper and add tests

frontend/package.json

@@ -21,7 +21,8 @@
   "scripts": {
     "start": "react-scripts start",
     "build": "react-scripts build",
-    "test": "echo 'no tests yet' # react-scripts test",
+    "test": "react-scripts test --watchAll=false",
+    "test:watch": "react-scripts test",
     "eject": "react-scripts eject"
   },
   "eslintConfig": {

frontend/src/App.test.tsx

@@ -1,9 +0,0 @@
-import React from 'react';
-import { render, screen } from '@testing-library/react';
-import App from './App';
-
-test('renders learn react link', () => {
-  render(<App />);
-  const linkElement = screen.getByText(/learn react/i);
-  expect(linkElement).toBeInTheDocument();
-});

frontend/src/helpers/millisFromDuration.test.ts

@@ -0,0 +1,13 @@
+import millisFromDuration from "./millisFromDuration";
+import { Duration } from '../generated/google/protobuf/duration';
+
+describe('millisFromDuration', () => {
+  it('returns 0 if duration is not passed', () => {
+    expect(millisFromDuration()).toEqual(0);
+  });
+
+  it('correctly returns the ms when the duration has both seconds and nanos', () => {
+    const duration: Duration = { seconds: 34, nanos: 549_875_992 };
+    expect(millisFromDuration(duration)).toEqual(34_549);
+  });
+});

frontend/src/helpers/millisFromDuration.ts

@@ -0,0 +1,10 @@
+import { Duration } from '../generated/google/protobuf/duration';
+
+function millisFromDuration(dur?: Duration): number {
+  if (dur == undefined) {
+    return 0;
+  }
+  return Math.floor(dur.seconds * 1000.0 + dur.nanos / 1000.0 / 1000.0);
+}
+
+export default millisFromDuration;