Add a spec for setting/updating a MR's milestone via the API

spec/requests/api/merge_requests_spec.rb

@@ -10,6 +10,7 @@ describe API::API, api: true  do
   let!(:merge_request_merged) { create(:merge_request, state: "merged", author: user, assignee: user, source_project: project, target_project: project, title: "Merged test", created_at: base_time + 2.seconds) }
   let!(:note) { create(:note_on_merge_request, author: user, project: project, noteable: merge_request, note: "a comment on a MR") }
   let!(:note2) { create(:note_on_merge_request, author: user, project: project, noteable: merge_request, note: "another comment on a MR") }
+  let(:milestone) { create(:milestone, title: '1.0.0', project: project) }
 
   before do
     project.team << [user, :reporters]
@@ -169,10 +170,12 @@ describe API::API, api: true  do
              source_branch: 'feature_conflict',
              target_branch: 'master',
              author: user,
-             labels: 'label, label2'
+             labels: 'label, label2',
+             milestone_id: milestone.id
         expect(response.status).to eq(201)
         expect(json_response['title']).to eq('Test merge_request')
         expect(json_response['labels']).to eq(['label', 'label2'])
+        expect(json_response['milestone']['id']).to eq(milestone.id)
       end
 
       it "should return 422 when source_branch equals target_branch" do
@@ -373,18 +376,24 @@ describe API::API, api: true  do
   end
 
   describe "PUT /projects/:id/merge_requests/:merge_request_id" do
-    it "should return merge_request" do
+    it "updates title and returns merge_request" do
       put api("/projects/#{project.id}/merge_requests/#{merge_request.id}", user), title: "New title"
       expect(response.status).to eq(200)
       expect(json_response['title']).to eq('New title')
     end
 
-    it "should return merge_request" do
+    it "updates description and returns merge_request" do
       put api("/projects/#{project.id}/merge_requests/#{merge_request.id}", user), description: "New description"
       expect(response.status).to eq(200)
       expect(json_response['description']).to eq('New description')
     end
 
+    it "updates milestone_id and returns merge_request" do
+      put api("/projects/#{project.id}/merge_requests/#{merge_request.id}", user), milestone_id: milestone.id
+      expect(response.status).to eq(200)
+      expect(json_response['milestone']['id']).to eq(milestone.id)
+    end
+
     it "should return 400 when source_branch is specified" do
       put api("/projects/#{project.id}/merge_requests/#{merge_request.id}", user),
       source_branch: "master", target_branch: "master"