Add a unittest check for proper motion correction

The loadPixelBox() funtion can be passed an epoch parameter, in which
case the reference catalog coordiantes are to up corrected for proper
motion (to the epoch provided).  This checks that this correction is
indeed being applied (using an extreme value for the epoch such that
the differences will be significant and reasnoably tested to have
changed via assertFloatsNotEqual).

tests/test_htmIndex.py

@@ -272,6 +272,16 @@ def testLoadPixelBox(self):
             cdMatrix = afwGeom.makeCdMatrix(scale=pixel_scale)
             wcs = afwGeom.makeSkyWcs(crval=cent, crpix=ctr_pix, cdMatrix=cdMatrix)
             result = loader.loadPixelBox(bbox=bbox, wcs=wcs, filterName="a")
+            # The following is to ensure the reference catalog coords are
+            # getting corrected for proper motion when an epoch is provided.
+            # Use an extreme epoch so that differences in corrected coords
+            # will be significant.
+            resultWithEpoch = loader.loadPixelBox(bbox=bbox, wcs=wcs, filterName="a",
+                                                  epoch=astropy.time.Time(20000, format='mjd', scale="tai"))
+            self.assertFloatsNotEqual(result.refCat["coord_ra"], resultWithEpoch.refCat["coord_ra"],
+                                      rtol=1.0e-4)
+            self.assertFloatsNotEqual(result.refCat["coord_dec"], resultWithEpoch.refCat["coord_dec"],
+                                      rtol=1.0e-4)
             self.assertFalse("camFlux" in result.refCat.schema)
             self.assertGreaterEqual(len(result.refCat), len(idList))
             numFound += len(result.refCat)