1 files changed, 89 insertions, 0 deletions
diff --git a/spec/lib/gitlab/usage/metrics/aggregates/sources/calculations/intersection_spec.rb b/spec/lib/gitlab/usage/metrics/aggregates/sources/calculations/intersection_spec.rb
new file mode 100644
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+++ b/spec/lib/gitlab/usage/metrics/aggregates/sources/calculations/intersection_spec.rb
@@ -0,0 +1,89 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Aggregates::Sources::Calculations::Intersection do
+  let_it_be(:recorded_at) { Time.current.to_i }
+  let_it_be(:start_date) { 4.weeks.ago.to_date }
+  let_it_be(:end_date) { Date.current }
+
+  shared_examples 'aggregated_metrics_data with source' do
+    context 'with AND operator' do
+      let(:params) { { start_date: start_date, end_date: end_date, recorded_at: recorded_at } }
+
+      context 'with even number of metrics' do
+        it 'calculates intersection correctly', :aggregate_failures do
+          # gmau_1 data is as follow
+          # |A| => 4
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: 'event3')).and_return(4)
+          # |B| => 6
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: 'event5')).and_return(6)
+          # |A + B| => 8
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: %w[event3 event5])).and_return(8)
+          # Exclusion inclusion principle formula to calculate intersection of 2 sets
+          # |A & B| = (|A| + |B|) - |A + B| => (4 + 6) - 8 => 2
+          expect(source.calculate_metrics_intersections(metric_names: %w[event3 event5], start_date: start_date, end_date: end_date, recorded_at: recorded_at)).to eq(2)
+        end
+      end
+
+      context 'with odd number of metrics' do
+        it 'calculates intersection correctly', :aggregate_failures do
+          # gmau_2 data is as follow:
+          # |A| => 2
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: 'event1')).and_return(2)
+          # |B| => 3
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: 'event2')).and_return(3)
+          # |C| => 5
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: 'event3')).and_return(5)
+
+          # |A + B| => 4 therefore |A & B| = (|A| + |B|) - |A + B| =>  2 + 3 - 4 => 1
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: %w[event1 event2])).and_return(4)
+          # |A + C| => 6 therefore |A & C| = (|A| + |C|) - |A + C| =>  2 + 5 - 6  => 1
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: %w[event1 event3])).and_return(6)
+          # |B + C| => 7 therefore |B & C| = (|B| + |C|) - |B + C| => 3 + 5 - 7 => 1
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: %w[event2 event3])).and_return(7)
+          # |A + B + C| => 8
+          expect(source).to receive(:calculate_metrics_union).with(params.merge(metric_names: %w[event1 event2 event3])).and_return(8)
+          # Exclusion inclusion principle formula to calculate intersection of 3 sets
+          # |A & B & C| = (|A & B| + |A & C| + |B & C|) - (|A| + |B| + |C|)  + |A + B + C|
+          # (1 + 1 + 1) - (2 + 3 + 5) + 8 => 1
+          expect(source.calculate_metrics_intersections(metric_names: %w[event1 event2 event3], start_date: start_date, end_date: end_date, recorded_at: recorded_at)).to eq(1)
+        end
+      end
+    end
+  end
+
+  describe '.aggregated_metrics_data' do
+    let(:source) do
+      Class.new do
+        extend Gitlab::Usage::Metrics::Aggregates::Sources::Calculations::Intersection
+      end
+    end
+
+    it 'caches intermediate operations', :aggregate_failures do
+      events = %w[event1 event2 event3 event5]
+
+      params = { start_date: start_date, end_date: end_date, recorded_at: recorded_at }
+
+      events.each do |event|
+        expect(source).to receive(:calculate_metrics_union)
+                                       .with(params.merge(metric_names: event))
+                                       .once
+                                       .and_return(0)
+      end
+
+      2.upto(4) do |subset_size|
+        events.combination(subset_size).each do |events|
+          expect(source).to receive(:calculate_metrics_union)
+                                         .with(params.merge(metric_names: events))
+                                         .once
+                                         .and_return(0)
+        end
+      end
+
+      expect(source.calculate_metrics_intersections(metric_names: events, start_date: start_date, end_date: end_date, recorded_at: recorded_at)).to eq(0)
+    end
+
+    it_behaves_like 'aggregated_metrics_data with source'
+  end
+end