test for 'coord exists' constraint (#5043)

Author: rcomer

lib/iris/tests/test_constraints.py

@@ -67,6 +67,27 @@ def test_constraints(self):
         sub_list = self.slices.extract(constraint)
         self.assertEqual(len(sub_list), 70 * 6)
 
+    def test_coord_availability(self):
+        # "model_level_number" coordinate available
+        constraint = iris.Constraint(model_level_number=lambda x: True)
+        result = self.slices.extract(constraint)
+        self.assertTrue(result)
+
+        # "wibble" coordinate is not available
+        constraint = iris.Constraint(wibble=lambda x: False)
+        result = self.slices.extract(constraint)
+        self.assertFalse(result)
+
+        # "wibble" coordinate is not available
+        constraint = iris.Constraint(wibble=lambda x: True)
+        result = self.slices.extract(constraint)
+        self.assertFalse(result)
+
+        # "lambda x: False" always (confusingly) throws away the cube
+        constraint = iris.Constraint(model_level_number=lambda x: False)
+        result = self.slices.extract(constraint)
+        self.assertFalse(result)
+
     def test_mismatched_type(self):
         constraint = iris.Constraint(model_level_number="aardvark")
         sub_list = self.slices.extract(constraint)