A very thorough article discussing how to convert a Chrome browser into an SEO testing environment, through a combination of browser settings and third-party add-ons. I personally like the idea of setting this up as a Chrome "profile", so you can load it and just begin testing, without resetting everything each time. Alternatively, the article suggests using Chrome Canary for the test bench.

In brief, this works by using the following steps:

• Install the User-Agent Switcher extension
• Grab the latest Googlebot user-agent string from the Chrome dev tools (Menu -> More Tools -> Network Conditions -> User Agent -> Uncheck "use browser default" -> Select "Googlebot" (or similar) from the dropdown -> Copy the string shown
• Add that string to User Agent Switcher as a new User Agent (Googlebot, paste string, Bots & Spiders, Replace, GB <-- these are the settings I used, can differ) and then select it from the plugin
  
• Disable service workers in the Chrome dev tools (Applications tab -> Service Workers -> Check "Bypass for Network")
• Disable local cache (Dev tools menu -> More Tools -> Network Conditions -> Check "Disable Cache")
• Disable all cookies (chrome://settings/cookies) and privacy-infringing APIs (chrome://settings/content) i.e. Location, Camera, Microphone, Notifications, and Background Sync
• Disable JavaScript (suggestion is to use the Web Developer extension)

They also suggest using a VPN to test from the US, as that is where Googlebot comes from. Similarly, the NoJS Side-by-Side bookmarklet is suggested as a good way to quickly test the site with JS running or not (seeing as Googlebot can now use JavaScript in some scenarios).