This was caused by a default `-1ns` which is no longer supported
in latest Kingpin.
The effect was that `kopia cache set` without
`--max-list-cache-duration` would fail. Unforutnately test was passing
that flag so it was missed.
This was likely caused by https://github.com/alecthomas/kingpin/pull/329
* cli: Added --max-examples-per-bucket flag to 'kopia snapshot estimate'
Added and cleaned up a bunch of unit tests.
Fixes#1054
* cli: misc tests to increase code coverage of the cli package
* ci: move code coverage run into separate GH job