1 files changed, 61 insertions, 0 deletions
diff --git a/spec/models/concerns/subquery_spec.rb b/spec/models/concerns/subquery_spec.rb
new file mode 100644
index 00000000000..95487fd8c2d
--- /dev/null
+++ b/spec/models/concerns/subquery_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Subquery do
+  let_it_be(:projects) { create_list :project, 3 }
+  let_it_be(:project_ids) { projects.map(&:id) }
+  let(:relation) { Project.where(id: projects) }
+
+  subject { relation.subquery(:id) }
+
+  shared_examples 'subquery as array values' do
+    specify { is_expected.to match_array project_ids }
+    specify { expect { subject }.not_to make_queries }
+  end
+
+  shared_examples 'subquery as relation' do
+    it { is_expected.to be_a ActiveRecord::Relation }
+    specify { expect { subject.load }.to make_queries }
+  end
+
+  shared_context 'when array size exceeds max_limit' do
+    subject { relation.subquery(:id, max_limit: 1) }
+  end
+
+  context 'when relation is not loaded' do
+    it_behaves_like 'subquery as relation'
+
+    context 'when array size exceeds max_limit' do
+      include_context 'when array size exceeds max_limit'
+
+      it_behaves_like 'subquery as relation'
+    end
+  end
+
+  context 'when relation is loaded' do
+    before do
+      relation.load
+    end
+
+    it_behaves_like 'subquery as array values'
+
+    context 'when array size exceeds max_limit' do
+      include_context 'when array size exceeds max_limit'
+
+      it_behaves_like 'subquery as relation'
+    end
+
+    context 'with a select' do
+      let(:relation) { Project.where(id: projects).select(:id) }
+
+      it_behaves_like 'subquery as array values'
+
+      context 'and querying with an unloaded column' do
+        subject { relation.subquery(:namespace_id) }
+
+        it { expect { subject }.to raise_error(ActiveModel::MissingAttributeError) }
+      end
+    end
+  end
+end