1 files changed, 65 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/count/tablesample_count_strategy_spec.rb b/spec/lib/gitlab/database/count/tablesample_count_strategy_spec.rb
new file mode 100644
index 00000000000..203f9344a41
--- /dev/null
+++ b/spec/lib/gitlab/database/count/tablesample_count_strategy_spec.rb
@@ -0,0 +1,65 @@
+require 'spec_helper'
+
+describe Gitlab::Database::Count::TablesampleCountStrategy do
+  before do
+    create_list(:project, 3)
+    create(:identity)
+  end
+
+  let(:models) { [Project, Identity] }
+  let(:strategy) { described_class.new(models) }
+
+  subject { strategy.count }
+
+  describe '#count', :postgresql do
+    let(:estimates) { { Project => threshold + 1, Identity => threshold - 1 } }
+    let(:threshold) { Gitlab::Database::Count::TablesampleCountStrategy::EXACT_COUNT_THRESHOLD }
+
+    before do
+      allow(strategy).to receive(:size_estimates).with(check_statistics: false).and_return(estimates)
+    end
+
+    context 'for tables with an estimated small size' do
+      it 'performs an exact count' do
+        expect(Identity).to receive(:count).and_call_original
+
+        expect(subject).to include({ Identity => 1 })
+      end
+    end
+
+    context 'for tables with an estimated large size' do
+      it 'performs a tablesample count' do
+        expect(Project).not_to receive(:count)
+
+        result = subject
+        expect(result[Project]).to eq(3)
+      end
+    end
+
+    context 'insufficient permissions' do
+      it 'returns an empty hash' do
+        allow(strategy).to receive(:size_estimates).and_raise(PG::InsufficientPrivilege)
+
+        expect(subject).to eq({})
+      end
+    end
+  end
+
+  describe '.enabled?' do
+    before do
+      stub_feature_flags(tablesample_counts: true)
+    end
+
+    it 'is enabled for PostgreSQL' do
+      allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
+
+      expect(described_class.enabled?).to be_truthy
+    end
+
+    it 'is disabled for MySQL' do
+      allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
+
+      expect(described_class.enabled?).to be_falsey
+    end
+  end
+end