diff --git a/spec/lib/gitlab/redis/hll_spec.rb b/spec/lib/gitlab/redis/hll_spec.rb
index 51768dd81c1..cbf78f23036 100644
--- a/spec/lib/gitlab/redis/hll_spec.rb
+++ b/spec/lib/gitlab/redis/hll_spec.rb
@@ -3,19 +3,104 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Redis::HLL, :clean_gitlab_redis_shared_state do
+  using RSpec::Parameterized::TableSyntax
+
+  let(:expiry) { 1.day }
+
   describe '.add' do
-    it 'raise an error when using an invalid key format' do
-      expect { described_class.add(key: 'test', value: 1, expiry: 1.day) }.to raise_error(Gitlab::Redis::HLL::KeyFormatError)
-      expect { described_class.add(key: 'test-{metric', value: 1, expiry: 1.day) }.to raise_error(Gitlab::Redis::HLL::KeyFormatError)
-      expect { described_class.add(key: 'test-{metric}}', value: 1, expiry: 1.day) }.to raise_error(Gitlab::Redis::HLL::KeyFormatError)
+    context 'when checking key format' do
+      context 'for invalid keys' do
+        where(:metric_key, :value) do
+          'test'           | 1
+          'test-{metric'   | 1
+          'test-{metric}}' | 1
+        end
+
+        with_them do
+          it 'raise an error when using an invalid key format' do
+            expect { described_class.add(key: metric_key, value: value, expiry: expiry) }.to raise_error(Gitlab::Redis::HLL::KeyFormatError)
+          end
+        end
+      end
+
+      context 'for valid keys' do
+        where(:metric_key, :value) do
+          'test-{metric}'                       | 1
+          'test-{metric}-1'                     | 1
+          'test:{metric}-1'                     | 1
+          '2020-216-{project_action}'           | 1
+          'i_{analytics}_dev_ops_score-2020-32' | 1
+        end
+
+        with_them do
+          it "doesn't raise error when having correct format" do
+            expect { described_class.add(key: metric_key, value: value, expiry: expiry) }.not_to raise_error
+          end
+        end
+      end
+    end
+  end
+
+  describe '.count' do
+    let(:event_2020_32) { '2020-32-{expand_vulnerabilities}' }
+    let(:event_2020_33) { '2020-33-{expand_vulnerabilities}' }
+    let(:event_2020_34) { '2020-34-{expand_vulnerabilities}' }
+
+    let(:entity1) { 'user_id_1'}
+    let(:entity2) { 'user_id_2'}
+    let(:entity3) { 'user_id_3'}
+    let(:entity4) { 'user_id_4'}
+
+    before do
+      track_event(event_2020_32, entity1)
+      track_event(event_2020_32, entity1)
+      track_event(event_2020_32, entity2)
+      track_event(event_2020_32, entity3)
+
+      track_event(event_2020_33, entity3)
+      track_event(event_2020_33, entity3)
+
+      track_event(event_2020_34, entity3)
+      track_event(event_2020_34, entity2)
     end
 
-    it "doesn't raise error when having correct format" do
-      expect { described_class.add(key: 'test-{metric}', value: 1, expiry: 1.day) }.not_to raise_error
-      expect { described_class.add(key: 'test-{metric}-1', value: 1, expiry: 1.day) }.not_to raise_error
-      expect { described_class.add(key: 'test:{metric}-1', value: 1, expiry: 1.day) }.not_to raise_error
-      expect { described_class.add(key: '2020-216-{project_action}', value: 1, expiry: 1.day) }.not_to raise_error
-      expect { described_class.add(key: 'i_{analytics}_dev_ops_score-2020-32', value: 1, expiry: 1.day) }.not_to raise_error
+    it 'has 3 distinct users for weeks 32, 33, 34' do
+      unique_counts = count_unique_events([event_2020_32, event_2020_33, event_2020_34])
+
+      expect(unique_counts).to eq(3)
+    end
+
+    it 'has 3 distinct users for weeks 32, 33' do
+      unique_counts = count_unique_events([event_2020_32, event_2020_33])
+
+      expect(unique_counts).to eq(3)
+    end
+
+    it 'has 2 distinct users for weeks 33, 34' do
+      unique_counts = count_unique_events([event_2020_33, event_2020_34])
+
+      expect(unique_counts).to eq(2)
+    end
+
+    it 'has one distinct user for week 33' do
+      unique_counts = count_unique_events([event_2020_33])
+
+      expect(unique_counts).to eq(1)
+    end
+
+    it 'has 4 distinct users when one different user has an action on week 34' do
+      track_event(event_2020_34, entity4, 29.days)
+      unique_counts = count_unique_events([event_2020_32, event_2020_33, event_2020_34])
+
+      expect(unique_counts).to eq(4)
+    end
+
+    def track_event(key, value, expiry = 1.day)
+      described_class.add(key: key, value: value, expiry: expiry)
+    end
+
+    def count_unique_events(keys)
+      described_class.count(keys: keys)
     end
   end
 end