1 files changed, 61 insertions, 0 deletions
diff --git a/spec/migrations/populate_merge_requests_latest_merge_request_diff_id_spec.rb b/spec/migrations/populate_merge_requests_latest_merge_request_diff_id_spec.rb
new file mode 100644
index 00000000000..4ea7f441f7c
--- /dev/null
+++ b/spec/migrations/populate_merge_requests_latest_merge_request_diff_id_spec.rb
@@ -0,0 +1,61 @@
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20171026082505_populate_merge_requests_latest_merge_request_diff_id')
+
+describe PopulateMergeRequestsLatestMergeRequestDiffId, :migration do
+  let(:projects_table) { table(:projects) }
+  let(:merge_requests_table) { table(:merge_requests) }
+  let(:merge_request_diffs_table) { table(:merge_request_diffs) }
+
+  let(:project) { projects_table.create!(name: 'gitlab', path: 'gitlab-org/gitlab-ce') }
+
+  def create_mr!(name, diffs: 0)
+    merge_request =
+      merge_requests_table.create!(target_project_id: project.id,
+                                   target_branch: 'master',
+                                   source_project_id: project.id,
+                                   source_branch: name,
+                                   title: name)
+
+    diffs.times do
+      merge_request_diffs_table.create!(merge_request_id: merge_request.id)
+    end
+
+    merge_request
+  end
+
+  def diffs_for(merge_request)
+    merge_request_diffs_table.where(merge_request_id: merge_request.id)
+  end
+
+  describe '#up' do
+    it 'ignores MRs without diffs' do
+      merge_request_without_diff = create_mr!('without_diff')
+
+      expect(merge_request_without_diff.latest_merge_request_diff_id).to be_nil
+
+      expect { migrate! }
+        .not_to change { merge_request_without_diff.reload.latest_merge_request_diff_id }
+    end
+
+    it 'ignores MRs that have a diff ID already set' do
+      merge_request_with_multiple_diffs = create_mr!('with_multiple_diffs', diffs: 3)
+      diff_id = diffs_for(merge_request_with_multiple_diffs).minimum(:id)
+
+      merge_request_with_multiple_diffs.update!(latest_merge_request_diff_id: diff_id)
+
+      expect { migrate! }
+        .not_to change { merge_request_with_multiple_diffs.reload.latest_merge_request_diff_id }
+    end
+
+    it 'migrates multiple MR diffs to the correct values' do
+      merge_requests = Array.new(3).map.with_index { |_, i| create_mr!(i, diffs: 3) }
+
+      migrate!
+
+      merge_requests.each do |merge_request|
+        expect(merge_request.reload.latest_merge_request_diff_id)
+          .to eq(diffs_for(merge_request).maximum(:id))
+      end
+    end
+  end
+end