1 files changed, 114 insertions, 0 deletions
diff --git a/spec/lib/gitlab/diff/file_collection/paginated_merge_request_diff_spec.rb b/spec/lib/gitlab/diff/file_collection/paginated_merge_request_diff_spec.rb
new file mode 100644
index 00000000000..74e5e667702
--- /dev/null
+++ b/spec/lib/gitlab/diff/file_collection/paginated_merge_request_diff_spec.rb
@@ -0,0 +1,114 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Diff::FileCollection::PaginatedMergeRequestDiff, feature_category: :code_review do
+  let(:merge_request) { create(:merge_request) }
+  let(:page) { 1 }
+  let(:per_page) { 10 }
+  let(:diffable) { merge_request.merge_request_diff }
+  let(:diff_files_relation) { diffable.merge_request_diff_files }
+  let(:diff_files) { subject.diff_files }
+
+  subject do
+    described_class.new(diffable,
+                        page,
+                        per_page)
+  end
+
+  describe '#diff_files' do
+    let(:per_page) { 3 }
+    let(:paginated_rel) { diff_files_relation.page(page).per(per_page) }
+
+    let(:expected_batch_files) do
+      paginated_rel.map(&:new_path)
+    end
+
+    it 'returns paginated diff files' do
+      expect(diff_files.size).to eq(3)
+    end
+
+    it 'returns a valid instance of a DiffCollection' do
+      expect(diff_files).to be_a(Gitlab::Git::DiffCollection)
+    end
+
+    context 'when first page' do
+      it 'returns correct diff files' do
+        expect(diff_files.map(&:new_path)).to eq(expected_batch_files)
+      end
+    end
+
+    context 'when another page' do
+      let(:page) { 2 }
+
+      it 'returns correct diff files' do
+        expect(diff_files.map(&:new_path)).to eq(expected_batch_files)
+      end
+    end
+
+    context 'when page is nil' do
+      let(:page) { nil }
+
+      it 'returns correct diff files' do
+        expected_batch_files =
+          diff_files_relation.page(described_class::DEFAULT_PAGE).per(per_page).map(&:new_path)
+
+        expect(diff_files.map(&:new_path)).to eq(expected_batch_files)
+      end
+    end
+
+    context 'when per_page is nil' do
+      let(:per_page) { nil }
+
+      it 'returns correct diff files' do
+        expected_batch_files =
+          diff_files_relation.page(page).per(described_class::DEFAULT_PER_PAGE).map(&:new_path)
+
+        expect(diff_files.map(&:new_path)).to eq(expected_batch_files)
+      end
+    end
+
+    context 'when invalid page' do
+      let(:page) { 999 }
+
+      it 'returns correct diff files' do
+        expect(diff_files.map(&:new_path)).to be_empty
+      end
+    end
+
+    context 'when last page' do
+      it 'returns correct diff files' do
+        last_page = diff_files_relation.count - per_page
+        collection = described_class.new(diffable,
+                                         last_page,
+                                         per_page)
+
+        expected_batch_files = diff_files_relation.page(last_page).per(per_page).map(&:new_path)
+
+        expect(collection.diff_files.map(&:new_path)).to eq(expected_batch_files)
+      end
+    end
+  end
+
+  it_behaves_like 'unfoldable diff' do
+    subject do
+      described_class.new(merge_request.merge_request_diff,
+                          page,
+                          per_page)
+    end
+  end
+
+  it_behaves_like 'cacheable diff collection' do
+    let(:cacheable_files_count) { per_page }
+  end
+
+  it_behaves_like 'unsortable diff files' do
+    let(:diffable) { merge_request.merge_request_diff }
+
+    subject do
+      described_class.new(merge_request.merge_request_diff,
+                          page,
+                          per_page)
+    end
+  end
+end