3 files changed, 91 insertions, 3 deletions

diff --git a/spec/models/concerns/manual_inverse_association_spec.rb b/spec/models/concerns/manual_inverse_association_spec.rb
new file mode 100644
index 00000000000..aad40883854
--- /dev/null
+++ b/spec/models/concerns/manual_inverse_association_spec.rb
@@ -0,0 +1,51 @@
+require 'spec_helper'
+
+describe ManualInverseAssociation do
+  let(:model) do
+    Class.new(MergeRequest) do
+      belongs_to :manual_association, class_name: 'MergeRequestDiff', foreign_key: :latest_merge_request_diff_id
+      manual_inverse_association :manual_association, :merge_request
+    end
+  end
+
+  before do
+    stub_const("#{described_class}::Model", model)
+  end
+
+  let(:instance) { create(:merge_request).becomes(model) }
+
+  describe '.manual_inverse_association' do
+    context 'when the relation exists' do
+      before do
+        instance.create_merge_request_diff
+        instance.reload
+      end
+
+      it 'loads the relation' do
+        expect(instance.manual_association).to be_an_instance_of(MergeRequestDiff)
+      end
+
+      it 'does not perform extra queries after loading' do
+        instance.manual_association
+
+        expect { instance.manual_association.merge_request }
+          .not_to exceed_query_limit(0)
+      end
+
+      it 'passes arguments to the default association method, to allow reloading' do
+        query_count = ActiveRecord::QueryRecorder.new do
+          instance.manual_association
+          instance.manual_association(true)
+        end.count
+
+        expect(query_count).to eq(2)
+      end
+    end
+
+    context 'when the relation does not return a value' do
+      it 'does not try to set an inverse' do
+        expect(instance.manual_association).to be_nil
+      end
+    end
+  end
+end
diff --git a/spec/models/merge_request_diff_spec.rb b/spec/models/merge_request_diff_spec.rb
index 0cfaa17676e..e2a9233a496 100644
--- a/spec/models/merge_request_diff_spec.rb
+++ b/spec/models/merge_request_diff_spec.rb
@@ -18,8 +18,8 @@ describe MergeRequestDiff do
     let!(:first_diff) { mr.merge_request_diff }
     let!(:last_diff) { mr.create_merge_request_diff }
 
-    it { expect(last_diff.latest?).to be_truthy }
-    it { expect(first_diff.latest?).to be_falsey }
+    it { expect(last_diff.reload).to be_latest }
+    it { expect(first_diff.reload).not_to be_latest }
   end
 
   describe '#diffs' do
@@ -29,7 +29,7 @@ describe MergeRequestDiff do
     context 'when the :ignore_whitespace_change option is set' do
       it 'creates a new compare object instead of loading from the DB' do
         expect(mr_diff).not_to receive(:load_diffs)
-        expect(Gitlab::Git::Compare).to receive(:new).and_call_original
+        expect(mr_diff.compare).to receive(:diffs).and_call_original
 
         mr_diff.raw_diffs(ignore_whitespace_change: true)
       end
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index d250ad50713..e510cc3ba47 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -79,6 +79,43 @@ describe MergeRequest do
     end
   end
 
+  describe '.set_latest_merge_request_diff_ids' do
+    def create_merge_request_with_diffs(source_branch, diffs: 2)
+      params = {
+        target_project: project,
+        target_branch: 'master',
+        source_project: project,
+        source_branch: source_branch
+      }
+
+      create(:merge_request, params).tap do |mr|
+        diffs.times { mr.merge_request_diffs.create }
+      end
+    end
+
+    let(:project) { create(:project) }
+
+    it 'sets IDs for merge requests, whether they are already set or not' do
+      merge_requests = [
+        create_merge_request_with_diffs('feature'),
+        create_merge_request_with_diffs('feature-conflict'),
+        create_merge_request_with_diffs('wip', diffs: 0),
+        create_merge_request_with_diffs('csv')
+      ]
+
+      merge_requests.take(2).each do |merge_request|
+        merge_request.update_column(:latest_merge_request_diff_id, nil)
+      end
+
+      expected = merge_requests.map do |merge_request|
+        merge_request.merge_request_diffs.maximum(:id)
+      end
+
+      expect { MergeRequest.set_latest_merge_request_diff_ids(project.merge_requests) }
+        .to change { merge_requests.map { |mr| mr.reload.latest_merge_request_diff_id } }.to(expected)
+    end
+  end
+
   describe '#target_branch_sha' do
     let(:project) { create(:project, :repository) }