1 files changed, 46 insertions, 0 deletions
diff --git a/spec/support/shared_examples/lib/gitlab/sql/set_operator_shared_examples.rb b/spec/support/shared_examples/lib/gitlab/sql/set_operator_shared_examples.rb
new file mode 100644
index 00000000000..73beef06855
--- /dev/null
+++ b/spec/support/shared_examples/lib/gitlab/sql/set_operator_shared_examples.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+RSpec.shared_examples 'SQL set operator' do |operator_keyword|
+  operator_keyword = operator_keyword.upcase
+
+  let(:relation_1) { User.where(email: 'alice@example.com').select(:id) }
+  let(:relation_2) { User.where(email: 'bob@example.com').select(:id) }
+
+  def to_sql(relation)
+    relation.reorder(nil).to_sql
+  end
+
+  describe '.operator_keyword' do
+    it { expect(described_class.operator_keyword).to eq operator_keyword }
+  end
+
+  describe '#to_sql' do
+    it "returns a String joining relations together using a #{operator_keyword}" do
+      set_operator = described_class.new([relation_1, relation_2])
+
+      expect(set_operator.to_sql).to eq("(#{to_sql(relation_1)})\n#{operator_keyword}\n(#{to_sql(relation_2)})")
+    end
+
+    it 'skips Model.none segements' do
+      empty_relation = User.none
+      set_operator = described_class.new([empty_relation, relation_1, relation_2])
+
+      expect {User.where("users.id IN (#{set_operator.to_sql})").to_a}.not_to raise_error
+      expect(set_operator.to_sql).to eq("(#{to_sql(relation_1)})\n#{operator_keyword}\n(#{to_sql(relation_2)})")
+    end
+
+    it "uses #{operator_keyword} ALL when removing duplicates is disabled" do
+      set_operator = described_class
+        .new([relation_1, relation_2], remove_duplicates: false)
+
+      expect(set_operator.to_sql).to include("#{operator_keyword} ALL")
+    end
+
+    it 'returns `NULL` if all relations are empty' do
+      empty_relation = User.none
+      set_operator = described_class.new([empty_relation, empty_relation])
+
+      expect(set_operator.to_sql).to eq('NULL')
+    end
+  end
+end