Add a Piff config test

tests/test_psf.py

@@ -335,6 +335,26 @@ def test_validatePsfCandidates(self, samplingSize):
         self.psfDeterminer._validatePsfCandidates(psfCandidateList, 21, samplingSize)
 
 
+class PiffConfigTestCase(lsst.utils.tests.TestCase):
+    """A test case to check for valid Piff config"""
+    def testValidateGalsimInterpolant(self):
+        # Check that random strings are not valid interpolants.
+        self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant("foo"))
+        # Check that the Lanczos order is an integer
+        self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant("Lanczos(3.0"))
+        self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant("Lanczos(-5.0"))
+        self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant("Lanczos(N)"))
+        # Check for various Lanczos interpolants
+        for interp in ("Lanczos(4)", "galsim.Lanczos(7)"):
+            self.assertTrue(PiffPsfDeterminerConfig.validateGalsimInterpolant(interp))
+            self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant(interp.lower()))
+        # Check that interpolation methods are case sensitive.
+        for interp in ("Linear", "Cubic", "Quintic", "SincInterpolant"):
+            self.assertTrue(PiffPsfDeterminerConfig.validateGalsimInterpolant(f"galsim.{interp}"))
+            self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant(f"galsim.{interp.lower()}"))
+            self.assertFalse(PiffPsfDeterminerConfig.validateGalsimInterpolant(interp))
+
+
 class TestMemory(lsst.utils.tests.MemoryTestCase):
     pass