1 files changed, 43 insertions, 0 deletions
diff --git a/spec/lib/gitlab/background_migration/backfill_merge_request_diffs_project_id_spec.rb b/spec/lib/gitlab/background_migration/backfill_merge_request_diffs_project_id_spec.rb
new file mode 100644
index 00000000000..8679a8fab8a
--- /dev/null
+++ b/spec/lib/gitlab/background_migration/backfill_merge_request_diffs_project_id_spec.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::BackgroundMigration::BackfillMergeRequestDiffsProjectId,
+  feature_category: :code_review_workflow,
+  schema: 20231114034017 do # schema before we introduced the invalid not-null constraint
+  let!(:tags_without_project_id) do
+    13.times do
+      namespace = table(:namespaces).create!(name: 'my namespace', path: 'my-namespace')
+      project = table(:projects).create!(name: 'my project', path: 'my-project', namespace_id: namespace.id,
+        project_namespace_id: namespace.id)
+      merge_request = table(:merge_requests).create!(target_project_id: project.id, target_branch: 'main',
+        source_branch: 'not-main')
+      table(:merge_request_diffs).create!(merge_request_id: merge_request.id, project_id: nil)
+    end
+  end
+
+  let!(:start_id) { table(:merge_request_diffs).minimum(:id) }
+  let!(:end_id) { table(:merge_request_diffs).maximum(:id) }
+
+  let!(:migration) do
+    described_class.new(
+      start_id: start_id,
+      end_id: end_id,
+      batch_table: :merge_request_diffs,
+      batch_column: :id,
+      sub_batch_size: 10,
+      pause_ms: 2,
+      connection: ::ApplicationRecord.connection
+    )
+  end
+
+  it 'backfills the missing project_id for the batch' do
+    backfilled_diffs = table(:merge_request_diffs)
+      .joins('INNER JOIN merge_requests ON merge_request_diffs.merge_request_id = merge_requests.id')
+      .where('merge_request_diffs.project_id = merge_requests.target_project_id')
+
+    expect do
+      migration.perform
+    end.to change { backfilled_diffs.count }.from(0).to(13)
+  end
+end