[test/validation] Add clear output method

Author: mpsonntag

test/test_validation_integration.py

@@ -28,6 +28,10 @@ def tearDown(self):
         sys.stdout = self.stdout_orig
         self.capture.close()
 
+    def _clear_output(self):
+        self.capture.seek(0)
+        self.capture.truncate()
+
     def _get_captured_output(self):
         out = [txt.strip() for txt in self.capture.getvalue().split('\n') if txt]
 
@@ -42,6 +46,9 @@ def test_property_values_cardinality(self):
         doc = odml.Document()
         sec = odml.Section(name="sec", type="sec_type", parent=doc)
 
+        # Making sure only the required warnings are tested
+        self._clear_output()
+
         # -- Test cardinality validation warnings on Property init
         # Test warning when setting invalid minimum
         _ = odml.Property(name="prop_card_min", values=[1], val_cardinality=(2, None), parent=sec)