This patch adds comprehensive tests for 'wendelin.lib.zodb.zstor_2zurl'.
Before this patch only one related test existed ('test_zurlstable').
This test only lightly checked correct functionality of 'zstor_2zurl'.
Therefore we added the new tests 'test_zstor_2zurl' and
'test_zurlsamedb'.

The new tests only cover existing functionality.

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Co-authored-by: kirr

/reviewed-by @kirr
/reviewed-on nexedi/wendelin.core!13