1 files changed, 70 insertions, 0 deletions
diff --git a/spec/lib/gitlab/diff/highlight_cache_spec.rb b/spec/lib/gitlab/diff/highlight_cache_spec.rb
new file mode 100644
index 00000000000..bfcfed4231f
--- /dev/null
+++ b/spec/lib/gitlab/diff/highlight_cache_spec.rb
@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Diff::HighlightCache do
+  let(:merge_request) { create(:merge_request_with_diffs) }
+
+  subject(:cache) { described_class.new(merge_request.diffs, backend: backend) }
+
+  describe '#decorate' do
+    let(:backend) { double('backend').as_null_object }
+
+    # Manually creates a Diff::File object to avoid triggering the cache on
+    # the FileCollection::MergeRequestDiff
+    let(:diff_file) do
+      diffs = merge_request.diffs
+      raw_diff = diffs.diffable.raw_diffs(diffs.diff_options.merge(paths: ['CHANGELOG'])).first
+      Gitlab::Diff::File.new(raw_diff,
+                             repository: diffs.project.repository,
+                             diff_refs: diffs.diff_refs,
+                             fallback_diff_refs: diffs.fallback_diff_refs)
+    end
+
+    it 'does not calculate highlighting when reading from cache' do
+      cache.write_if_empty
+      cache.decorate(diff_file)
+
+      expect_any_instance_of(Gitlab::Diff::Highlight).not_to receive(:highlight)
+
+      diff_file.highlighted_diff_lines
+    end
+
+    it 'assigns highlighted diff lines to the DiffFile' do
+      cache.write_if_empty
+      cache.decorate(diff_file)
+
+      expect(diff_file.highlighted_diff_lines.size).to be > 5
+    end
+
+    it 'submits a single reading from the cache' do
+      cache.decorate(diff_file)
+      cache.decorate(diff_file)
+
+      expect(backend).to have_received(:read).with(cache.key).once
+    end
+  end
+
+  describe '#write_if_empty' do
+    let(:backend) { double('backend', read: {}).as_null_object }
+
+    it 'submits a single writing to the cache' do
+      cache.write_if_empty
+      cache.write_if_empty
+
+      expect(backend).to have_received(:write).with(cache.key,
+                                                    hash_including('CHANGELOG-false-false-false'),
+                                                    expires_in: 1.week).once
+    end
+  end
+
+  describe '#clear' do
+    let(:backend) { double('backend').as_null_object }
+
+    it 'clears cache' do
+      cache.clear
+
+      expect(backend).to have_received(:delete).with(cache.key)
+    end
+  end
+end