1 files changed, 109 insertions, 0 deletions
diff --git a/spec/metrics_server/metrics_server_spec.rb b/spec/metrics_server/metrics_server_spec.rb
new file mode 100644
index 00000000000..4e3c6900875
--- /dev/null
+++ b/spec/metrics_server/metrics_server_spec.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+require_relative '../../metrics_server/metrics_server'
+require_relative '../support/helpers/next_instance_of'
+
+RSpec.describe MetricsServer do # rubocop:disable RSpec/FilePath
+  include NextInstanceOf
+
+  before do
+    # We do not want this to have knock-on effects on the test process.
+    allow(Gitlab::ProcessManagement).to receive(:modify_signals)
+  end
+
+  describe '.spawn' do
+    context 'when in parent process' do
+      it 'forks into a new process and detaches it' do
+        expect(Process).to receive(:fork).and_return(99)
+        expect(Process).to receive(:detach).with(99)
+
+        described_class.spawn('sidekiq', metrics_dir: 'path/to/metrics')
+      end
+    end
+
+    context 'when in child process' do
+      before do
+        # This signals the process that it's "inside" the fork
+        expect(Process).to receive(:fork).and_return(nil)
+        expect(Process).not_to receive(:detach)
+      end
+
+      it 'starts the metrics server with the given arguments' do
+        expect_next_instance_of(MetricsServer) do |server|
+          expect(server).to receive(:start)
+        end
+
+        described_class.spawn('sidekiq', metrics_dir: 'path/to/metrics')
+      end
+
+      it 'resets signal handlers from parent process' do
+        expect(Gitlab::ProcessManagement).to receive(:modify_signals).with(%i[A B], 'DEFAULT')
+
+        described_class.spawn('sidekiq', metrics_dir: 'path/to/metrics', trapped_signals: %i[A B])
+      end
+    end
+  end
+
+  describe '#start' do
+    let(:exporter_class) { Class.new(Gitlab::Metrics::Exporter::BaseExporter) }
+    let(:exporter_double) { double('fake_exporter', start: true) }
+    let(:prometheus_config) { ::Prometheus::Client.configuration }
+    let(:metrics_dir) { Dir.mktmpdir }
+    let(:settings) { { "fake_exporter" => { "enabled" => true } } }
+    let!(:old_metrics_dir) { prometheus_config.multiprocess_files_dir }
+
+    subject(:metrics_server) { described_class.new('fake', metrics_dir, true)}
+
+    before do
+      stub_const('Gitlab::Metrics::Exporter::FakeExporter', exporter_class)
+      expect(exporter_class).to receive(:instance).with(settings['fake_exporter'], synchronous: true).and_return(exporter_double)
+      expect(Settings).to receive(:monitoring).and_return(settings)
+    end
+
+    after do
+      Gitlab::Metrics.reset_registry!
+      FileUtils.rm_rf(metrics_dir, secure: true)
+      prometheus_config.multiprocess_files_dir = old_metrics_dir
+    end
+
+    it 'configures ::Prometheus::Client' do
+      metrics_server.start
+
+      expect(prometheus_config.multiprocess_files_dir).to eq metrics_dir
+    end
+
+    it 'ensures that metrics directory exists in correct mode (0700)' do
+      expect(FileUtils).to receive(:mkdir_p).with(metrics_dir, mode: 0700)
+
+      metrics_server.start
+    end
+
+    context 'when wipe_metrics_dir is true' do
+      subject(:metrics_server) { described_class.new('fake', metrics_dir, true)}
+
+      it 'removes any old metrics files' do
+        FileUtils.touch("#{metrics_dir}/remove_this.db")
+
+        expect { metrics_server.start }.to change { Dir.empty?(metrics_dir) }.from(false).to(true)
+      end
+    end
+
+    context 'when wipe_metrics_dir is false' do
+      subject(:metrics_server) { described_class.new('fake', metrics_dir, false)}
+
+      it 'does not remove any old metrics files' do
+        FileUtils.touch("#{metrics_dir}/remove_this.db")
+
+        expect { metrics_server.start }.not_to change { Dir.empty?(metrics_dir) }.from(false)
+      end
+    end
+
+    it 'starts a metrics server' do
+      expect(exporter_double).to receive(:start)
+
+      metrics_server.start
+    end
+  end
+end