1 files changed, 81 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..58556d2cf5a
--- /dev/null
+++ b/spec/metrics_server/metrics_server_spec.rb
@@ -0,0 +1,81 @@
+# 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
+
+  describe '.spawn' do
+    let(:env) do
+      {
+        'METRICS_SERVER_TARGET' => 'sidekiq',
+        'GITLAB_CONFIG' => nil
+      }
+    end
+
+    it 'spawns a process with the correct environment variables and detaches it' do
+      expect(Process).to receive(:spawn).with(env, anything, err: $stderr, out: $stdout).and_return(99)
+      expect(Process).to receive(:detach).with(99)
+
+      described_class.spawn('sidekiq')
+    end
+  end
+
+  describe '#start' do
+    let(:exporter_class) { Class.new(Gitlab::Metrics::Exporter::BaseExporter) }
+    let(:exporter_double) { double('fake_exporter', start: true) }
+    let(:prometheus_client_double) { double(::Prometheus::Client) }
+    let(:prometheus_config) { ::Prometheus::Client::Configuration.new }
+    let(:metrics_dir) { Dir.mktmpdir }
+    let(:settings_double) { double(:settings, sidekiq_exporter: {}) }
+
+    subject(:metrics_server) { described_class.new('fake', metrics_dir)}
+
+    before do
+      stub_env('prometheus_multiproc_dir', metrics_dir)
+      stub_const('Gitlab::Metrics::Exporter::FakeExporter', exporter_class)
+      allow(exporter_class).to receive(:instance).with({}, synchronous: true).and_return(exporter_double)
+      allow(Settings).to receive(:monitoring).and_return(settings_double)
+    end
+
+    after do
+      Dir.rmdir(metrics_dir)
+    end
+
+    it 'configures ::Prometheus::Client' do
+      allow(prometheus_client_double).to receive(:configuration).and_return(prometheus_config)
+
+      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
+
+    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
+
+    it 'starts a metrics server' do
+      expect(exporter_double).to receive(:start)
+
+      metrics_server.start
+    end
+
+    it 'sends the correct Settings to the exporter instance' do
+      expect(Settings).to receive(:monitoring).and_return(settings_double)
+      expect(settings_double).to receive(:sidekiq_exporter)
+
+      metrics_server.start
+    end
+  end
+end