1 files changed, 119 insertions, 0 deletions
diff --git a/spec/lib/gitlab/metrics/sampler_spec.rb b/spec/lib/gitlab/metrics/sampler_spec.rb
new file mode 100644
index 00000000000..27211350fbe
--- /dev/null
+++ b/spec/lib/gitlab/metrics/sampler_spec.rb
@@ -0,0 +1,119 @@
+require 'spec_helper'
+
+describe Gitlab::Metrics::Sampler do
+  let(:sampler) { described_class.new(5) }
+
+  after do
+    Allocations.stop if Gitlab::Metrics.mri?
+  end
+
+  describe '#start' do
+    it 'gathers a sample at a given interval' do
+      expect(sampler).to receive(:sleep).with(5)
+      expect(sampler).to receive(:sample)
+      expect(sampler).to receive(:loop).and_yield
+
+      sampler.start.join
+    end
+  end
+
+  describe '#sample' do
+    it 'samples various statistics' do
+      expect(sampler).to receive(:sample_memory_usage)
+      expect(sampler).to receive(:sample_file_descriptors)
+      expect(sampler).to receive(:sample_objects)
+      expect(sampler).to receive(:sample_gc)
+      expect(sampler).to receive(:flush)
+
+      sampler.sample
+    end
+
+    it 'clears any GC profiles' do
+      expect(sampler).to receive(:flush)
+      expect(GC::Profiler).to receive(:clear)
+
+      sampler.sample
+    end
+  end
+
+  describe '#flush' do
+    it 'schedules the metrics using Sidekiq' do
+      expect(Gitlab::Metrics).to receive(:submit_metrics).
+        with([an_instance_of(Hash)])
+
+      sampler.sample_memory_usage
+      sampler.flush
+    end
+  end
+
+  describe '#sample_memory_usage' do
+    it 'adds a metric containing the memory usage' do
+      expect(Gitlab::Metrics::System).to receive(:memory_usage).
+        and_return(9000)
+
+      expect(sampler).to receive(:add_metric).
+        with(/memory_usage/, value: 9000).
+        and_call_original
+
+      sampler.sample_memory_usage
+    end
+  end
+
+  describe '#sample_file_descriptors' do
+    it 'adds a metric containing the amount of open file descriptors' do
+      expect(Gitlab::Metrics::System).to receive(:file_descriptor_count).
+        and_return(4)
+
+      expect(sampler).to receive(:add_metric).
+        with(/file_descriptors/, value: 4).
+        and_call_original
+
+      sampler.sample_file_descriptors
+    end
+  end
+
+  describe '#sample_objects' do
+    it 'adds a metric containing the amount of allocated objects' do
+      expect(sampler).to receive(:add_metric).
+        with(/object_counts/, an_instance_of(Hash), an_instance_of(Hash)).
+        at_least(:once).
+        and_call_original
+
+      sampler.sample_objects
+    end
+  end
+
+  describe '#sample_gc' do
+    it 'adds a metric containing garbage collection statistics' do
+      expect(GC::Profiler).to receive(:total_time).and_return(0.24)
+
+      expect(sampler).to receive(:add_metric).
+        with(/gc_statistics/, an_instance_of(Hash)).
+        and_call_original
+
+      sampler.sample_gc
+    end
+  end
+
+  describe '#add_metric' do
+    it 'prefixes the series name for a Rails process' do
+      expect(sampler).to receive(:sidekiq?).and_return(false)
+
+      expect(Gitlab::Metrics::Metric).to receive(:new).
+        with('rails_cats', { value: 10 }, {}).
+        and_call_original
+
+      sampler.add_metric('cats', value: 10)
+    end
+
+    it 'prefixes the series name for a Sidekiq process' do
+      expect(sampler).to receive(:sidekiq?).and_return(true)
+
+      expect(Gitlab::Metrics::Metric).to receive(:new).
+        with('sidekiq_cats', { value: 10 }, {}).
+        and_call_original
+
+      sampler.add_metric('cats', value: 10)
+    end
+  end
+end