1 files changed, 96 insertions, 0 deletions
diff --git a/spec/lib/gitlab/graphql/loaders/issuable_loader_spec.rb b/spec/lib/gitlab/graphql/loaders/issuable_loader_spec.rb
new file mode 100644
index 00000000000..180966de895
--- /dev/null
+++ b/spec/lib/gitlab/graphql/loaders/issuable_loader_spec.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Graphql::Loaders::IssuableLoader do
+  subject { described_class.new(parent, finder) }
+
+  let(:params) { HashWithIndifferentAccess.new }
+
+  describe '#find_all' do
+    let(:finder) { double(:finder, params: params, execute: %i[x y z]) }
+
+    where(:factory, :param_name) do
+      %i[project group].map { |thing| [thing, :"#{thing}_id"] }
+    end
+
+    with_them do
+      let(:parent) { build_stubbed(factory) }
+
+      it 'assignes the parent parameter, and batching_find_alls the finder' do
+        expect(subject.find_all).to contain_exactly(:x, :y, :z)
+        expect(params).to include(param_name => parent)
+      end
+    end
+
+    context 'the parent is of an unexpected type' do
+      let(:parent) { build(:merge_request) }
+
+      it 'raises an error if we pass an unexpected parent' do
+        expect { subject.find_all }.to raise_error(/Unexpected parent/)
+      end
+    end
+  end
+
+  describe '#batching_find_all' do
+    context 'the finder params are anything other than [iids]' do
+      let(:finder) { double(:finder, params: params, execute: [:foo]) }
+      let(:parent) { build_stubbed(:project) }
+
+      it 'batching_find_alls the finder, setting the correct parent parameter' do
+        expect(subject.batching_find_all).to eq([:foo])
+        expect(params[:project_id]).to eq(parent)
+      end
+
+      it 'allows a post-process block' do
+        expect(subject.batching_find_all(&:first)).to eq(:foo)
+      end
+    end
+
+    context 'the finder params are exactly [iids]' do
+      # Dumb finder class, that only implements what we need, and has
+      # predictable query counts.
+      let(:finder_class) do
+        Class.new do
+          attr_reader :current_user, :params
+
+          def initialize(user, args)
+            @current_user = user
+            @params = HashWithIndifferentAccess.new(args.to_h)
+          end
+
+          def execute
+            params[:project_id].issues.where(iid: params[:iids])
+          end
+        end
+      end
+
+      it 'batches requests' do
+        issue_a = create(:issue)
+        issue_b = create(:issue)
+        issue_c = create(:issue, project: issue_a.project)
+        proj_1 = issue_a.project
+        proj_2 = issue_b.project
+        user = create(:user, developer_projects: [proj_1, proj_2])
+
+        finder_a = finder_class.new(user, iids: [issue_a.iid])
+        finder_b = finder_class.new(user, iids: [issue_b.iid])
+        finder_c = finder_class.new(user, iids: [issue_c.iid])
+
+        results = []
+
+        expect do
+          results.concat(described_class.new(proj_1, finder_a).batching_find_all)
+          results.concat(described_class.new(proj_2, finder_b).batching_find_all)
+          results.concat(described_class.new(proj_1, finder_c).batching_find_all)
+        end.not_to exceed_query_limit(0)
+
+        expect do
+          results = results.map(&:sync)
+        end.not_to exceed_query_limit(2)
+
+        expect(results).to contain_exactly(issue_a, issue_b, issue_c)
+      end
+    end
+  end
+end