1 files changed, 75 insertions, 0 deletions
diff --git a/spec/migrations/20210708130419_reschedule_merge_request_diff_users_background_migration_spec.rb b/spec/migrations/20210708130419_reschedule_merge_request_diff_users_background_migration_spec.rb
new file mode 100644
index 00000000000..9cc454662f9
--- /dev/null
+++ b/spec/migrations/20210708130419_reschedule_merge_request_diff_users_background_migration_spec.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration! 'reschedule_merge_request_diff_users_background_migration'
+
+RSpec.describe RescheduleMergeRequestDiffUsersBackgroundMigration, :migration do
+  let(:migration) { described_class.new }
+
+  describe '#up' do
+    before do
+      allow(described_class::MergeRequestDiff)
+        .to receive(:minimum)
+        .with(:id)
+        .and_return(42)
+
+      allow(described_class::MergeRequestDiff)
+        .to receive(:maximum)
+        .with(:id)
+        .and_return(85_123)
+    end
+
+    it 'deletes existing background migration job records' do
+      args = [150_000, 300_000]
+
+      Gitlab::Database::BackgroundMigrationJob
+        .create!(class_name: described_class::MIGRATION_NAME, arguments: args)
+
+      migration.up
+
+      found = Gitlab::Database::BackgroundMigrationJob
+        .where(class_name: described_class::MIGRATION_NAME, arguments: args)
+        .count
+
+      expect(found).to eq(0)
+    end
+
+    it 'schedules the migrations in batches' do
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(2.minutes.to_i, described_class::MIGRATION_NAME, [42, 40_042])
+
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(4.minutes.to_i, described_class::MIGRATION_NAME, [40_042, 80_042])
+
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(6.minutes.to_i, described_class::MIGRATION_NAME, [80_042, 120_042])
+
+      migration.up
+    end
+
+    it 'creates rows to track the background migration jobs' do
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [42, 40_042])
+
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [40_042, 80_042])
+
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [80_042, 120_042])
+
+      migration.up
+    end
+  end
+end