Add test checking method closed_without_source_project

app/controllers/projects/merge_requests_controller.rb

@@ -428,17 +428,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def validates_merge_request
-    # If source project was removed (Ex. mr from fork to origin)
-    # return invalid_mr unless @merge_request.source_project
-
     # Show git not found page
     # if there is no saved commits between source & target branch
     if @merge_request.commits.blank?
       # and if target branch doesn't exist
       return invalid_mr unless @merge_request.target_branch_exists?
-
-      # or if source branch doesn't exist
-      # return invalid_mr unless @merge_request.source_branch_exists?
     end
   end
 

spec/models/merge_request_spec.rb

@@ -1038,4 +1038,42 @@ describe MergeRequest, models: true do
       end
     end
   end
+
+  describe "#closed_without_source_project?" do
+    let(:project)      { create(:project) }
+    let(:fork_project) { create(:project, forked_from_project: project) }
+    let(:user)         { create(:user) }
+    let(:destroy_project) { Projects::DestroyService.new(fork_project, user, {}) }
+
+    context "when the merge request is closed" do
+      let(:closed_merge_request) do
+        create(:closed_merge_request,
+          source_project: fork_project,
+          target_project: project)
+      end
+
+      it "returns false if the source project exist" do
+        expect(closed_merge_request.closed_without_source_project?).to be_falsey
+      end
+
+      it "returns true if the source project does not exist" do
+        destroy_project.async_execute
+        closed_merge_request.reload
+
+        expect(closed_merge_request.closed_without_source_project?).to be_truthy
+      end
+    end
+
+    context "when the merge request is open" do
+      let(:open_merge_request) do
+        create(:merge_request,
+          source_project: fork_project,
+          target_project: project)
+      end
+
+      it "returns false" do
+        expect(open_merge_request.closed_without_source_project?).to be_falsey
+      end
+    end
+  end
 end