Optimize queries and pagination in `GroupDescendantsFinder`

1 files changed, 46 insertions, 0 deletions

diff --git a/spec/lib/gitlab/multi_collection_paginator_spec.rb b/spec/lib/gitlab/multi_collection_paginator_spec.rb
new file mode 100644
index 00000000000..385cfa63dda
--- /dev/null
+++ b/spec/lib/gitlab/multi_collection_paginator_spec.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+describe Gitlab::MultiCollectionPaginator do
+  subject(:paginator) { described_class.new(Project.all, Group.all, per_page: 3) }
+
+  it 'combines both collections' do
+    project = create(:project)
+    group = create(:group)
+
+    expect(paginator.paginate(1)).to eq([project, group])
+  end
+
+  it 'includes elements second collection if first collection is empty' do
+    group = create(:group)
+
+    expect(paginator.paginate(1)).to eq([group])
+  end
+
+  context 'with a full first page' do
+    let!(:all_groups) { create_list(:group, 4) }
+    let!(:all_projects) { create_list(:project, 4) }
+
+    it 'knows the total count of the collection' do
+      expect(paginator.total_count).to eq(8)
+    end
+
+    it 'fills the first page with elements of the first collection' do
+      expect(paginator.paginate(1)).to eq(all_projects.take(3))
+    end
+
+    it 'fils the second page with a mixture of of the first & second collection' do
+      first_collection_element = all_projects.last
+      second_collection_elements = all_groups.take(2)
+
+      expected_collection = [first_collection_element] + second_collection_elements
+
+      expect(paginator.paginate(2)).to eq(expected_collection)
+    end
+
+    it 'fils the last page with elements from the second collection' do
+      expected_collection = all_groups[-2..-1]
+
+      expect(paginator.paginate(3)).to eq(expected_collection)
+    end
+  end
+end