align_wcs to raise custom exception when not enough inputs

[mcara]

Closes #202

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.77%. Comparing base (4ab4c69) to head (fd5641c).
Report is 84 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
+ Coverage   85.91%   93.77%   +7.85%     
==========================================
  Files           9       11       +2     
  Lines        1754     1992     +238     
  Branches      272        0     -272     
==========================================
+ Hits         1507     1868     +361     
+ Misses        242      124     -118     
+ Partials        5        0       -5     

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[braingram]

Thanks!

These test could be updated to check for the new exception:

tweakwcs/tweakwcs/tests/test_imalign.py

Lines 29 to 32 in fb46242

	with pytest.raises(ValueError) as e:
	align_wcs([tpwcs, tpwcs, tpwcs])
	assert e.value.args[0] == ("Too few input images (or groups of images) "
	"with non-empty catalogs.")

and this one:

tweakwcs/tweakwcs/tests/test_imalign.py

Lines 475 to 477 in fb46242

	with pytest.raises(ValueError) as e:
	align_wcs(tpwcs, refcat=None, fitgeom='shift', match=None)
	assert e.value.args[0] == ("Too few input images (or groups of images) "

[braingram]

LGTM!