Function drain

test/unit/session_composition_test.js:21–31

(times = 5, ms = 700)

// (added while the chain runs) are surfaced. Returns the last error seen, or
// undefined if the chain settled cleanly.
async function drain(times = 5, ms = 700) {
  let err
  for (let i = 0; i < times; i++) {
    try {
      await settles(Promise.resolve(recorder.promise()), ms)
    } catch (e) {
      err = e
    }
  }
  return err
}

function makeFakeHelper() {
  const calls = { start: 0, stop: 0, loadVars: 0, restoreVars: 0, withinBegin: 0, withinEnd: 0 }