All work is in meas_astrom on tickets/DM-2740. In addition to making ANetAstrometryTask's solver a subtask, but also added a plotter for matches and made a few other minor cleanups.

• Making the solver a subtask is a very good thing.
• I don't know if it is compatible with the unit tests' design policy but it would be good to be able to pass the "doPlot" as an option when running the test on the command line.
• In astrometry.py::_matchAndFitWCS in the if block displaying the "TAN-SIP WCS" match : https://github.com/lsst/meas_astrom/blob/tickets/DM-2740/python/lsst/meas/astrom/astrometry.py#L298 it would be better to plot the goodSources instead of the sources, in this way, one could see which sources have been rejected.

I like your suggestion to display good sources instead of all sources in _matchAndFitWCS. I handled it slightly differently:

• I renamed "clean" sources to "usable" sources, which I think is a clearer name. These may be saturated but they may also be used to by the matcher, so I think they are what should be plotted.
• I return the usable sources from the matcher and plot them in _matchAndFitWCS

Your suggestion of making "doPlot" a command-line argument to some tests is a good one, but I'm not ready to implement it yet. The problem is that I find I usually only want to display plots for a single test method (rather than all in a suite). Thus I don't think a simple boolean command-line argument would offer enough control. For now I'm happier forcing users to tweak the test before running it.