More specs for fallback testing.

lib/gitlab/database/count.rb

@@ -29,6 +29,9 @@ module Gitlab
         strategies.each_with_object({}) do |strategy, counts_by_model|
           if strategy.enabled?
             models_with_missing_counts = models - counts_by_model.keys
+
+            return counts_by_model if models_with_missing_counts.empty?
+
             counts = strategy.new(models_with_missing_counts).count
 
             counts.each do |model, count|

spec/lib/gitlab/database/count_spec.rb

@@ -27,6 +27,39 @@ describe Gitlab::Database::Count do
     end
 
     context 'fallbacks' do
+      subject { described_class.approximate_counts(models, strategies: strategies) }
+
+      let(:strategies) do
+        [
+          double('s1', :enabled? => true, new: first_strategy),
+          double('s2', :enabled? => true, new: second_strategy)
+        ]
+      end
+
+      let(:first_strategy) { double('first strategy', count: {}) }
+      let(:second_strategy) { double('second strategy', count: {}) }
+
+      it 'gets results from first strategy' do
+        expect(strategies[0]).to receive(:new).with(models).and_return(first_strategy)
+        expect(first_strategy).to receive(:count)
+
+        subject
+      end
+
+      it 'gets more results from second strategy if some counts are missing' do
+        expect(first_strategy).to receive(:count).and_return({ Project => 3 })
+        expect(strategies[1]).to receive(:new).with([Identity]).and_return(second_strategy)
+        expect(second_strategy).to receive(:count).and_return({ Identity => 1 })
+
+        expect(subject).to eq({ Project => 3, Identity => 1 })
+      end
+
+      it 'does not get more results as soon as all counts are present' do
+        expect(first_strategy).to receive(:count).and_return({ Project => 3, Identity => 1 })
+        expect(strategies[1]).not_to receive(:new)
+
+        subject
+      end
     end
 
     context 'with PostgreSQL', :postgresql do