Added checks for migration downtime

These new checks can be used to check if migrations require downtime or
not (as tagged by their authors). In CI this compares the current branch
with master so migrations added by merge requests are automatically
verified.

To check the migrations added since a Git reference simply run:

    bundle exec rake gitlab:db:downtime_check[GIT_REF]

1 files changed, 113 insertions, 0 deletions

diff --git a/spec/lib/gitlab/downtime_check_spec.rb b/spec/lib/gitlab/downtime_check_spec.rb
new file mode 100644
index 00000000000..42d895e548e
--- /dev/null
+++ b/spec/lib/gitlab/downtime_check_spec.rb
@@ -0,0 +1,113 @@
+require 'spec_helper'
+
+describe Gitlab::DowntimeCheck do
+  subject { described_class.new }
+  let(:path) { 'foo.rb' }
+
+  describe '#check' do
+    before do
+      expect(subject).to receive(:require).with(path)
+    end
+
+    context 'when a migration does not specify if downtime is required' do
+      it 'raises RuntimeError' do
+        expect(subject).to receive(:class_for_migration_file).
+          with(path).
+          and_return(Class.new)
+
+        expect { subject.check([path]) }.
+          to raise_error(RuntimeError, /it requires downtime/)
+      end
+    end
+
+    context 'when a migration requires downtime' do
+      context 'when no reason is specified' do
+        it 'raises RuntimeError' do
+          stub_const('TestMigration::DOWNTIME', true)
+
+          expect(subject).to receive(:class_for_migration_file).
+            with(path).
+            and_return(TestMigration)
+
+          expect { subject.check([path]) }.
+            to raise_error(RuntimeError, /no reason was given/)
+        end
+      end
+
+      context 'when a reason is specified' do
+        it 'returns an Array of messages' do
+          stub_const('TestMigration::DOWNTIME', true)
+          stub_const('TestMigration::DOWNTIME_REASON', 'foo')
+
+          expect(subject).to receive(:class_for_migration_file).
+            with(path).
+            and_return(TestMigration)
+
+          messages = subject.check([path])
+
+          expect(messages).to be_an_instance_of(Array)
+          expect(messages[0]).to be_an_instance_of(Gitlab::DowntimeCheck::Message)
+
+          message = messages[0]
+
+          expect(message.path).to eq(path)
+          expect(message.offline).to eq(true)
+          expect(message.reason).to eq('foo')
+        end
+      end
+    end
+  end
+
+  describe '#check_and_print' do
+    it 'checks the migrations and prints the results to STDOUT' do
+      stub_const('TestMigration::DOWNTIME', true)
+      stub_const('TestMigration::DOWNTIME_REASON', 'foo')
+
+      expect(subject).to receive(:require).with(path)
+
+      expect(subject).to receive(:class_for_migration_file).
+        with(path).
+        and_return(TestMigration)
+
+      expect(subject).to receive(:puts).with(an_instance_of(String))
+
+      subject.check_and_print([path])
+    end
+  end
+
+  describe '#class_for_migration_file' do
+    it 'returns the class for a migration file path' do
+      expect(subject.class_for_migration_file('123_string.rb')).to eq(String)
+    end
+  end
+
+  describe '#online?' do
+    it 'returns true when a migration can be performed online' do
+      stub_const('TestMigration::DOWNTIME', false)
+
+      expect(subject.online?(TestMigration)).to eq(true)
+    end
+
+    it 'returns false when a migration can not be performed online' do
+      stub_const('TestMigration::DOWNTIME', true)
+
+      expect(subject.online?(TestMigration)).to eq(false)
+    end
+  end
+
+  describe '#downtime_reason' do
+    context 'when a reason is defined' do
+      it 'returns the downtime reason' do
+        stub_const('TestMigration::DOWNTIME_REASON', 'hello')
+
+        expect(subject.downtime_reason(TestMigration)).to eq('hello')
+      end
+    end
+
+    context 'when a reason is not defined' do
+      it 'returns nil' do
+        expect(subject.downtime_reason(Class.new)).to be_nil
+      end
+    end
+  end
+end