Return error message for create_merge_request

app/controllers/projects/issues_controller.rb

@@ -186,7 +186,7 @@ class Projects::IssuesController < Projects::ApplicationController
     if result[:status] == :success
       render json: MergeRequestCreateSerializer.new.represent(result[:merge_request])
     else
-      render json: result[:messsage], status: :unprocessable_entity
+      render json: result[:message], status: :unprocessable_entity
     end
   end
 

changelogs/unreleased/merge-request-typo.yml

+---
+title: Return error message for create_merge_request
+merge_request: 28482
+author:
+type: fixed

spec/controllers/projects/issues_controller_spec.rb

@@ -1249,6 +1249,26 @@ describe Projects::IssuesController do
       expect(response).to have_gitlab_http_status(:not_found)
     end
 
+    context 'invalid branch name' do
+      it 'is unprocessable' do
+        post(
+          :create_merge_request,
+          params: {
+            target_project_id: nil,
+            branch_name: 'master',
+            ref: 'master',
+            namespace_id: project.namespace.to_param,
+            project_id: project.to_param,
+            id: issue.to_param
+          },
+          format: :json
+        )
+
+        expect(response.body).to eq('Branch already exists')
+        expect(response).to have_gitlab_http_status(:unprocessable_entity)
+      end
+    end
+
     context 'target_project_id is set' do
       let(:target_project) { fork_project(project, user, repository: true) }
       let(:target_project_id) { target_project.id }