1 files changed, 109 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/migrations/runner_spec.rb b/spec/lib/gitlab/database/migrations/runner_spec.rb
new file mode 100644
index 00000000000..52fb5ec2ba8
--- /dev/null
+++ b/spec/lib/gitlab/database/migrations/runner_spec.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::Migrations::Runner do
+  let(:result_dir) { Pathname.new(Dir.mktmpdir) }
+
+  let(:migration_runs) { [] } # This list gets populated as the runner tries to run migrations
+
+  # Tests depend on all of these lists being sorted in the order migrations would be applied
+  let(:applied_migrations_other_branches) { [double(ActiveRecord::Migration, version: 1, name: 'migration_complete_other_branch')] }
+
+  let(:applied_migrations_this_branch) do
+    [
+      double(ActiveRecord::Migration, version: 2, name: 'older_migration_complete_this_branch'),
+      double(ActiveRecord::Migration, version: 3, name: 'newer_migration_complete_this_branch')
+    ].sort_by(&:version)
+  end
+
+  let(:pending_migrations) do
+    [
+      double(ActiveRecord::Migration, version: 4, name: 'older_migration_pending'),
+      double(ActiveRecord::Migration, version: 5, name: 'newer_migration_pending')
+    ].sort_by(&:version)
+  end
+
+  before do
+    stub_const('Gitlab::Database::Migrations::Runner::BASE_RESULT_DIR', result_dir)
+    allow(ActiveRecord::Migrator).to receive(:new) do |dir, _all_migrations, _schema_migration_class, version_to_migrate|
+      migrator = double(ActiveRecord::Migrator)
+      expect(migrator).to receive(:run) do
+        migration_runs << OpenStruct.new(dir: dir, version_to_migrate: version_to_migrate)
+      end
+      migrator
+    end
+
+    all_versions = (applied_migrations_other_branches + applied_migrations_this_branch).map(&:version)
+    migrations = applied_migrations_other_branches + applied_migrations_this_branch + pending_migrations
+    ctx = double(ActiveRecord::MigrationContext, get_all_versions: all_versions, migrations: migrations, schema_migration: ActiveRecord::SchemaMigration)
+
+    allow(described_class).to receive(:migration_context).and_return(ctx)
+
+    names_this_branch = (applied_migrations_this_branch + pending_migrations).map { |m| "db/migrate/#{m.version}_#{m.name}.rb"}
+    allow(described_class).to receive(:migration_file_names_this_branch).and_return(names_this_branch)
+  end
+
+  after do
+    FileUtils.rm_rf(result_dir)
+  end
+
+  it 'creates the results dir when one does not exist' do
+    FileUtils.rm_rf(result_dir)
+
+    expect do
+      described_class.new(direction: :up, migrations: [], result_dir: result_dir).run
+    end.to change { Dir.exist?(result_dir) }.from(false).to(true)
+  end
+
+  describe '.up' do
+    context 'result directory' do
+      it 'uses the /up subdirectory' do
+        expect(described_class.up.result_dir).to eq(result_dir.join('up'))
+      end
+    end
+
+    context 'migrations to run' do
+      subject(:up) { described_class.up }
+
+      it 'is the list of pending migrations' do
+        expect(up.migrations).to eq(pending_migrations)
+      end
+    end
+
+    context 'running migrations' do
+      subject(:up) { described_class.up }
+
+      it 'runs the unapplied migrations in version order', :aggregate_failures do
+        up.run
+
+        expect(migration_runs.map(&:dir)).to eq([:up, :up])
+        expect(migration_runs.map(&:version_to_migrate)).to eq(pending_migrations.map(&:version))
+      end
+    end
+  end
+
+  describe '.down' do
+    subject(:down) { described_class.down }
+
+    context 'result directory' do
+      it 'is the /down subdirectory' do
+        expect(down.result_dir).to eq(result_dir.join('down'))
+      end
+    end
+
+    context 'migrations to run' do
+      it 'is the list of migrations that are up and on this branch' do
+        expect(down.migrations).to eq(applied_migrations_this_branch)
+      end
+    end
+
+    context 'running migrations' do
+      it 'runs the applied migrations for the current branch in reverse order', :aggregate_failures do
+        down.run
+
+        expect(migration_runs.map(&:dir)).to eq([:down, :down])
+        expect(migration_runs.map(&:version_to_migrate)).to eq(applied_migrations_this_branch.reverse.map(&:version))
+      end
+    end
+  end
+end