Add browser tests

Author: Simran-B

tests/browser/browser.js

@@ -168,3 +168,45 @@ async function getLocationObject (page) {
   })
   return JSON.parse(location)
 }
+
+describe('platform specific content', () => {
+  // from tests/javascripts/user-agent.js
+  const userAgents = [
+    { name: 'Mac', id: 'mac', ua: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_2) AppleWebKit/601.3.9 (KHTML, like Gecko) Version/9.0.2 Safari/601.3.9' },
+    { name: 'Windows', id: 'windows', ua: 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.111 Safari/537.36' },
+    { name: 'Linux', id: 'linux', ua: 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:15.0) Gecko/20100101 Firefox/15.0.1' },
+  ]
+  const userAgentLinux = userAgents[2]
+
+  it('should have a platform switcher', async () => {
+    await page.goto('http://localhost:4001/en/actions/hosting-your-own-runners/configuring-the-self-hosted-runner-application-as-a-service')
+    const nav = await page.$$('nav.UnderlineNav')
+    const switches = await page.$$('a.platform-switcher')
+    const selectedSwitch = await page.$$('a.platform-switcher.selected')
+    expect(nav.length).toEqual(1)
+    expect(switches.length).toBeGreaterThan(1)
+    expect(selectedSwitch.length).toEqual(1)
+  })
+
+  it('should detect platform from user agent', async () => {
+    for (const agent of userAgents) {
+      await page.setUserAgent(agent.ua)
+      await page.goto('http://localhost:4001/en/actions/hosting-your-own-runners/monitoring-and-troubleshooting-self-hosted-runners')
+      const selectedPlatformElement = await page.waitForSelector('a.platform-switcher.selected')
+      const selectedPlatform = await page.evaluate( el => el.textContent, selectedPlatformElement)
+      expect(selectedPlatform).toBe(agent.name)
+    }
+  })
+
+  it('should prefer defaultPlatform from frontmatter', async () => {
+    for (const agent of userAgents) {
+      await page.setUserAgent(agent.ua)
+      await page.goto('http://localhost:4001/en/actions/hosting-your-own-runners/configuring-the-self-hosted-runner-application-as-a-service')
+      const defaultPlatform = await page.$eval('[data-default-platform]', el => el.dataset.defaultPlatform)
+      const selectedPlatformElement = await page.waitForSelector('a.platform-switcher.selected')
+      const selectedPlatform = await page.evaluate( el => el.textContent, selectedPlatformElement)
+      expect(defaultPlatform).toBe(userAgentLinux.id)
+      expect(selectedPlatform).toBe(userAgentLinux.name)
+    }
+  })
+})