Replace test_field_distortion.py

tests/test_field_distortion.py

@@ -186,7 +186,7 @@ def field_distortion_model(
             iccdKey = "ccd" + str("0%d" % (iccd))[-2:]
 
             # load PSF data
-            ipsfDatn = cat_dir + "ccd%d_%s.dat" % (iccd, iwaveKey)
+            ipsfDatn = os.path.join(cat_dir, "ccd%d_%s.dat" % (iccd, iwaveKey))
             ipsfDat = Table.read(ipsfDatn, format="ascii")
             for ipsf in range(1, npsf + 1):
                 # if ipsf!=2: continue