1 files changed, 86 insertions, 0 deletions
diff --git a/spec/services/ci/prometheus_metrics/observe_histograms_service_spec.rb b/spec/services/ci/prometheus_metrics/observe_histograms_service_spec.rb
new file mode 100644
index 00000000000..2eef852b0f4
--- /dev/null
+++ b/spec/services/ci/prometheus_metrics/observe_histograms_service_spec.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Ci::PrometheusMetrics::ObserveHistogramsService do
+  let_it_be(:project) { create(:project) }
+  let(:params) { {} }
+
+  subject(:execute) { described_class.new(project, params).execute }
+
+  before do
+    Gitlab::Metrics.reset_registry!
+  end
+
+  context 'with empty data' do
+    it 'does not raise errors' do
+      is_expected.to be_success
+    end
+  end
+
+  context 'observes metrics successfully' do
+    let(:params) do
+      {
+        histograms: [
+          { name: 'pipeline_graph_link_calculation_duration_seconds', value: '1' },
+          { name: 'pipeline_graph_links_per_job_ratio', value: '0.9' }
+        ]
+      }
+    end
+
+    it 'increments the metrics' do
+      execute
+
+      expect(histogram_data).to match(a_hash_including({ 0.8 => 0.0, 1 => 1.0, 2 => 1.0 }))
+
+      expect(histogram_data(:pipeline_graph_links_per_job_ratio))
+        .to match(a_hash_including({ 0.8 => 0.0, 0.9 => 1.0, 1 => 1.0 }))
+    end
+
+    it 'returns an empty body and status code' do
+      is_expected.to be_success
+      expect(subject.http_status).to eq(:created)
+      expect(subject.payload).to eq({})
+    end
+  end
+
+  context 'with unknown histograms' do
+    let(:params) do
+      { histograms: [{ name: 'chunky_bacon', value: '4' }] }
+    end
+
+    it 'raises ActiveRecord::RecordNotFound error' do
+      expect { subject }.to raise_error ActiveRecord::RecordNotFound
+    end
+  end
+
+  context 'with feature flag disabled' do
+    before do
+      stub_feature_flags(ci_accept_frontend_prometheus_metrics: false)
+    end
+
+    let(:params) do
+      {
+        histograms: [
+          { name: 'pipeline_graph_link_calculation_duration_seconds', value: '4' }
+        ]
+      }
+    end
+
+    it 'does not register the metrics' do
+      execute
+
+      expect(histogram_data).to be_nil
+    end
+
+    it 'returns an empty body and status code' do
+      is_expected.to be_success
+      expect(subject.http_status).to eq(:accepted)
+      expect(subject.payload).to eq({})
+    end
+  end
+
+  def histogram_data(name = :pipeline_graph_link_calculation_duration_seconds)
+    Gitlab::Metrics.registry.get(name)&.get({})
+  end
+end