1 files changed, 69 insertions, 0 deletions
diff --git a/spec/migrations/slice_merge_request_diff_commit_migrations_spec.rb b/spec/migrations/slice_merge_request_diff_commit_migrations_spec.rb
new file mode 100644
index 00000000000..1fd19ee42b4
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+++ b/spec/migrations/slice_merge_request_diff_commit_migrations_spec.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration! 'slice_merge_request_diff_commit_migrations'
+
+RSpec.describe SliceMergeRequestDiffCommitMigrations, :migration do
+  let(:migration) { described_class.new }
+
+  describe '#up' do
+    context 'when there are no jobs to process' do
+      it 'does nothing' do
+        expect(migration).not_to receive(:migrate_in)
+        expect(Gitlab::Database::BackgroundMigrationJob).not_to receive(:create!)
+
+        migration.up
+      end
+    end
+
+    context 'when there are pending jobs' do
+      let!(:job1) do
+        Gitlab::Database::BackgroundMigrationJob.create!(
+          class_name: described_class::MIGRATION_CLASS,
+          arguments: [1, 10_001]
+        )
+      end
+
+      let!(:job2) do
+        Gitlab::Database::BackgroundMigrationJob.create!(
+          class_name: described_class::MIGRATION_CLASS,
+          arguments: [10_001, 20_001]
+        )
+      end
+
+      it 'marks the old jobs as finished' do
+        migration.up
+
+        job1.reload
+        job2.reload
+
+        expect(job1).to be_succeeded
+        expect(job2).to be_succeeded
+      end
+
+      it 'the jobs are slices into smaller ranges' do
+        migration.up
+
+        new_jobs = Gitlab::Database::BackgroundMigrationJob
+          .for_migration_class(described_class::MIGRATION_CLASS)
+          .pending
+          .to_a
+
+        expect(new_jobs.map(&:arguments)).to eq([
+          [1, 5_001],
+          [5_001, 10_001],
+          [10_001, 15_001],
+          [15_001, 20_001]
+        ])
+      end
+
+      it 'schedules a background migration for the first job' do
+        expect(migration)
+          .to receive(:migrate_in)
+          .with(1.hour, described_class::STEAL_MIGRATION_CLASS, [1, 5_001])
+
+        migration.up
+      end
+    end
+  end
+end