When calculating the queue position in
`GetProvisionerJobsByIDsWithQueuePosition` we only counted jobs with
`started_at = NULL`. This is misleading, as it allows canceling or
canceled jobs to take up rows in the computed queue position, giving an
impression that the queue is larger than it really is.
This modifies the query to also exclude jobs with a null `canceled_at`,
`completed_at`, or `error` field for the purposes of calculating the
queue position, and also adds a test to validate this behaviour.
(Note: due to the behaviour of `dbgen.ProvisionerJob` with `dbmem` I had
to use other proxy methods to validate the corresponding dbmem
implementation.)
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Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>
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