I believe this is causing the failures we are seeing in CI. Specifically because we rely on process.env.CI to be set so that we use the correct configuration for chrome (to avoid the setuid errors). See our default generated testem.js for how that works.

Can you tweak this to stash off the value and restore it instead? Something like:

let ORIGINAL_PROCESS_ENV_CI;
beforeEach(function() {
  // ...snip...
  ORIGINAL_PROCESS_ENV_CI = process.env.CI;
});

afterEach(function() {
  if (ORIGINAL_PROCESS_ENV_CI === undefined) {
    delete process.env.CI;
  } else {
    process.env.CI = ORIGINAL_PROCESS_ENV_CI;
  }
});