We've been developing a pattern in recent changes to normalize the

results of a SCMClient.diff() operation for comparison in unit tests,

changing timestamps into something stable. Both the Perforce and Bazaar

support have implemented their own version of this _normalize_diff()

function. Upcoming changes for CVS need this as well, but with a

different timestamp format.
This introduces SCMClientTestCase.normalize_diff_result(), which now

handles the normalization but accepts variations in the timestamp

format. It takes an optional date_format= argument containing values

that would be passed to strftime(), and turns (some) flags into

patterns for a regex used to transform dates.
Bazaar and Perforce tests have been updated to use this.

Unit tests pass on Python 3.7-3.11.