My reading of the first test is that it should fail:

* given that the duration is 300 ms,
* if we hit the website at time *t* we set `createdAt = t`
* then if we visit the site at *t + 400 ms*,
* `expiresAt = createdAt + duration = t + 300` which is less than `now = t + 400`

Am I seeing this wrong?