Only cache highlight results for latest MR diffs

Previously, we kept them all in the cache. We don't need the highlight results
for older diffs - if someone does view that (which is rare), we can do the
highlighting on the fly.

1 files changed, 28 insertions, 8 deletions

diff --git a/spec/services/merge_requests/merge_request_diff_cache_service_spec.rb b/spec/services/merge_requests/merge_request_diff_cache_service_spec.rb
index bb46e1dd9ab..33cba7225e3 100644
--- a/spec/services/merge_requests/merge_request_diff_cache_service_spec.rb
+++ b/spec/services/merge_requests/merge_request_diff_cache_service_spec.rb
@@ -1,19 +1,39 @@
 require 'spec_helper'
 
-describe MergeRequests::MergeRequestDiffCacheService do
+describe MergeRequests::MergeRequestDiffCacheService, :use_clean_rails_memory_store_caching do
   let(:subject) { described_class.new }
+  let(:merge_request) { create(:merge_request) }
 
   describe '#execute' do
-    it 'retrieves the diff files to cache the highlighted result' do
-      merge_request = create(:merge_request)
-      cache_key = [merge_request.merge_request_diff, 'highlighted-diff-files', Gitlab::Diff::FileCollection::MergeRequestDiff.default_options]
-
-      expect(Rails.cache).to receive(:read).with(cache_key).and_return({})
-      expect(Rails.cache).to receive(:write).with(cache_key, anything)
+    before do
       allow_any_instance_of(Gitlab::Diff::File).to receive(:text?).and_return(true)
       allow_any_instance_of(Gitlab::Diff::File).to receive(:diffable?).and_return(true)
+    end
+
+    it 'retrieves the diff files to cache the highlighted result' do
+      new_diff = merge_request.merge_request_diff
+      cache_key = new_diff.diffs.cache_key
+
+      expect(Rails.cache).to receive(:read).with(cache_key).and_call_original
+      expect(Rails.cache).to receive(:write).with(cache_key, anything).and_call_original
+
+      subject.execute(merge_request, new_diff)
+    end
+
+    it 'clears the cache for older diffs on the merge request' do
+      old_diff = merge_request.merge_request_diff
+      old_cache_key = old_diff.diffs.cache_key
+
+      subject.execute(merge_request, old_diff)
+
+      new_diff = merge_request.create_merge_request_diff
+      new_cache_key = new_diff.diffs.cache_key
+
+      expect(Rails.cache).to receive(:delete).with(old_cache_key).and_call_original
+      expect(Rails.cache).to receive(:read).with(new_cache_key).and_call_original
+      expect(Rails.cache).to receive(:write).with(new_cache_key, anything).and_call_original
 
-      subject.execute(merge_request)
+      subject.execute(merge_request, new_diff)
     end
   end
 end