add tests

app/assets/javascripts/views/forms/form.js

@@ -16,12 +16,12 @@ document.addEventListener("DOMContentLoaded", function () {
 
     if(hidden_input){
         hidden_input.classList.remove('hidden');
-    };
+    }
 
     var visible_input = document.getElementById(visible_input_id);
     if(visible_input){
         visible_input.classList.add('hidden');
-    };
+    }
   };
 
   if (is_reducer_form) {

app/controllers/reducers_controller.rb

@@ -141,7 +141,10 @@ def record_not_valid(exception)
   def remove_unwanted_config_key(param_object)
     if param_object[:topic] == 'reduce_by_subject'
       param_object[:subject_reducer_keys] = nil
-    elsif
+    elsif param_object[:topic] == 'reduce_by_user'
+      param_object[:user_reducer_keys] = nil
+    else
+      param_object[:subject_reducer_keys] = nil
       param_object[:user_reducer_keys] = nil
     end
   end

spec/controllers/reducers_controller_spec.rb

@@ -147,6 +147,34 @@
                               reducer: {key: nil, type: 'external'}}
         expect(response.status).to eq(200)
       end
+
+      context 'when topic is reduce_by_subject' do
+        it 'sets subject_reducer_keys to nil' do
+          put :update, params: {
+            workflow_id: workflow.id,
+            id: reducer.id,
+            reducer: {url: 'https://example.org/2', user_reducer_keys: 'user_reducer_keys_value', subject_reducer_keys: 'subject_reducer_keys',topic: 'reduce_by_subject'},
+          }
+
+          reducer.reload
+          expect(reducer.subject_reducer_keys).to be_nil
+          expect(reducer.user_reducer_keys).to eq('user_reducer_keys_value')
+        end
+      end
+
+      context 'when topic is not reduce_by_subject' do
+        it 'sets user_reducer_keys to nil' do
+          put :update, params: {
+            workflow_id: workflow.id,
+            id: reducer.id,
+            reducer: {url: 'https://example.org/2', user_reducer_keys: 'user_reducer_keys_value', subject_reducer_keys: 'subject_reducer_keys_value',topic: 'reduce_by_user'},
+          }
+
+          reducer.reload
+          expect(reducer.subject_reducer_keys).to eq('subject_reducer_keys_value')
+          expect(reducer.user_reducer_keys).to be_nil
+        end
+      end
     end
   end
 end