Make handling missing instances in test helpers more explicit

tests/test_integration/test_postgras_api.py

@@ -126,22 +126,24 @@ def docker_setup(request, tmpdir):
 class PostgraasApiTestBase:
     def get_postgraas_by_name(self, name, client):
         headers = {'Content-Type': 'application/json'}
-        list = client.get('/api/v2/postgraas_instances', headers=headers)
-        for instance in json.loads(list.get_data(as_text=True)):
+        instances = client.get('/api/v2/postgraas_instances', headers=headers)
+        for instance in json.loads(instances.get_data(as_text=True)):
             if instance["postgraas_instance_name"] == name:
                 return instance["id"]
+        return None
 
     def delete_instance_by_name(self, db_credentials, client):
-        id = self.get_postgraas_by_name(db_credentials["postgraas_instance_name"], client)
-        db_pwd = db_credentials["db_pwd"]
-        headers = {'Content-Type': 'application/json'}
-        client.delete(
-            '/api/v2/postgraas_instances/' + str(id),
-            data=json.dumps({
-                'db_pwd': db_pwd
-            }),
-            headers=headers
-        )
+        instance_id = self.get_postgraas_by_name(db_credentials["postgraas_instance_name"], client)
+        if instance_id is not None:
+            db_pwd = db_credentials["db_pwd"]
+            headers = {'Content-Type': 'application/json'}
+            client.delete(
+                '/api/v2/postgraas_instances/' + str(instance_id),
+                data=json.dumps({
+                    'db_pwd': db_pwd
+                }),
+                headers=headers
+            )
 
 
 @pytest.mark.usefixtures('docker_setup')