Add spec for scheduling migration

db/post_migrate/20200127111840_fix_projects_without_project_feature.rb

@@ -4,6 +4,7 @@ class FixProjectsWithoutProjectFeature < ActiveRecord::Migration[5.2]
   include Gitlab::Database::MigrationHelpers
 
   BATCH_SIZE = 50_000
+  MIGRATION = 'FixProjectsWithoutProjectFeature'
 
   disable_ddl_transaction!
 
@@ -12,7 +13,7 @@ class FixProjectsWithoutProjectFeature < ActiveRecord::Migration[5.2]
   end
 
   def up
-    queue_background_migration_jobs_by_range_at_intervals(Project, 'FixProjectsWithoutProjectFeature', 2.minutes, batch_size: BATCH_SIZE)
+    queue_background_migration_jobs_by_range_at_intervals(Project, MIGRATION, 2.minutes, batch_size: BATCH_SIZE)
   end
 
   def down

spec/migrations/fix_projects_without_project_feature_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200127111840_fix_projects_without_project_feature.rb')
+
+describe FixProjectsWithoutProjectFeature, :migration do
+  let(:namespace) { table(:namespaces).create(name: 'gitlab', path: 'gitlab-org') }
+
+  let!(:projects) do
+    [
+      table(:projects).create(namespace_id: namespace.id, name: 'foo 1'),
+      table(:projects).create(namespace_id: namespace.id, name: 'foo 2'),
+      table(:projects).create(namespace_id: namespace.id, name: 'foo 3')
+    ]
+  end
+
+  before do
+    stub_const("#{described_class.name}::BATCH_SIZE", 2)
+  end
+
+  around do |example|
+    Sidekiq::Testing.fake! do
+      Timecop.freeze do
+        example.call
+      end
+    end
+  end
+
+  it 'schedules jobs for ranges of projects' do
+    migrate!
+
+    expect(described_class::MIGRATION)
+      .to be_scheduled_delayed_migration(2.minutes, projects[0].id, projects[1].id)
+
+    expect(described_class::MIGRATION)
+      .to be_scheduled_delayed_migration(4.minutes, projects[2].id, projects[2].id)
+  end
+
+  it 'schedules jobs according to the configured batch size' do
+    expect { migrate! }.to change { BackgroundMigrationWorker.jobs.size }.by(2)
+  end
+end