Unfortunately, there seems to be no built-in way that I can find.
If you want a quick and dirty solution, I recommend the following:
Available browsers in testem defined in testem/lib/browser_launcher.js If you want to modify a file that uses ember-cli , this will be the full path:
<your-app-dir>/node_modules/ember-cli/node_modules/testem/lib/browser_launcher.js
This file has a browsersForPlatform() function. Find your platform and entry for Chrome. For Darwin, the corresponding entry is as follows:
{ name: "Chrome", exe: "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome", args: ["--user-data-dir=" + tempDir + "/testem.chrome", "--no-default-browser-check", "--no-first-run", "--ignore-certificate-errors"], setup: function(config, done){ rimraf(tempDir + '/testem.chrome', done) }, supported: browserExeExists },
You want to change args so that it is called as you like. My guess is that --user-data-dir points to the tmp directory. Perhaps just fixing it will solve the problem.
Ideally, testem will suggest a way to override browser settings in the testem.json file. This is likely to be a fairly simple contribution to the testem project, if you are interested, and there is interest among those involved.
If you follow the path of changing browser_launcher.js , just remember that it will crash every time the node package is updated. I assume that you can install the branched version and then keep your copy up to date as you see fit.