1 files changed, 29 insertions, 0 deletions
diff --git a/spec/lib/gitlab/usage/metrics/aggregates/sources/redis_hll_spec.rb b/spec/lib/gitlab/usage/metrics/aggregates/sources/redis_hll_spec.rb
new file mode 100644
index 00000000000..af2de5ea343
--- /dev/null
+++ b/spec/lib/gitlab/usage/metrics/aggregates/sources/redis_hll_spec.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Aggregates::Sources::RedisHll do
+  describe '.calculate_events_union' do
+    let(:event_names) { %w[event_a event_b] }
+    let(:start_date) { 7.days.ago }
+    let(:end_date) { Date.current }
+
+    subject(:calculate_metrics_union) do
+      described_class.calculate_metrics_union(metric_names: event_names, start_date: start_date, end_date: end_date, recorded_at: nil)
+    end
+
+    it 'calls Gitlab::UsageDataCounters::HLLRedisCounter.calculate_events_union' do
+      expect(Gitlab::UsageDataCounters::HLLRedisCounter).to receive(:calculate_events_union)
+                                                              .with(event_names: event_names, start_date: start_date, end_date: end_date)
+                                                              .and_return(5)
+
+      calculate_metrics_union
+    end
+
+    it 'prevents from using fallback value as valid union result' do
+      allow(Gitlab::UsageDataCounters::HLLRedisCounter).to receive(:calculate_events_union).and_return(-1)
+
+      expect { calculate_metrics_union }.to raise_error Gitlab::Usage::Metrics::Aggregates::Sources::UnionNotAvailable
+    end
+  end
+end