I added checks against testing.Short for tests that took longer than
about one second on my machine. Running with -short reduces the test
time of light from about 21s to about 0.9s.
Our test cases spew a lot of files and directories around $TMPDIR. Make more
thorough use of the testing package's TempDir methods to ensure these are
cleaned up.
In a few cases, this required plumbing test contexts through existing helper
code. In a couple places an explicit path was required, to work around cases
where we do global setup during a TestMain function. Those cases probably
deserve more thorough cleansing (preferably with fire), but for now I have just
worked around it to keep focused on the cleanup.
* Allow for zero witness providers
* Verify provider duplicates, fix tests
* Add duplicate provider ID to the error
* Return error on attempt to remove last witness
* Verify duplicates when restoring from store
