basically: you call `this.sinon.useFakeTimers()` in setup,

then you can move the clock by using `this.sinon.clock.tick(nb_ms)`, so here it would be `this.sinon.clock.tick(100)` (the SAVE_STATE_WAIT_TIMEOUT constant is equal to 100ms in grid.js).

What's good with this, it's that your test is made linear and synchronous. You don't need a `done` callback anymore, and this is faster.