1 files changed, 83 insertions, 0 deletions
diff --git a/spec/lib/gitlab/git/cross_repo_spec.rb b/spec/lib/gitlab/git/cross_repo_spec.rb
new file mode 100644
index 00000000000..09a28c144a4
--- /dev/null
+++ b/spec/lib/gitlab/git/cross_repo_spec.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Git::CrossRepo do
+  let_it_be(:source_project) { create(:project, :repository) }
+  let_it_be(:target_project) { create(:project, :repository) }
+
+  let(:source_repo) { source_project.repository.raw_repository }
+  let(:target_repo) { target_project.repository.raw_repository }
+
+  let(:source_branch) { 'feature' }
+  let(:target_branch) { target_repo.root_ref }
+
+  let(:source_commit) { source_repo.commit(source_branch) }
+  let(:target_commit) { source_repo.commit(target_branch) }
+
+  def execute(&block)
+    described_class.new(source_repo, target_repo).execute(target_branch, &block)
+  end
+
+  describe '#execute' do
+    context 'when executed within a single repository' do
+      let(:target_project) { source_project }
+
+      it 'does not fetch from another repo' do
+        expect(source_repo).not_to receive(:fetch_source_branch!)
+
+        expect { |block| execute(&block) }.to yield_with_args(target_branch)
+      end
+    end
+
+    context 'when executed across two repositories' do
+      context 'and target ref exists in source repo' do
+        it 'does not fetch from another repo' do
+          expect(source_repo).not_to receive(:fetch_source_branch!)
+          expect(source_repo).not_to receive(:delete_refs)
+
+          expect { |block| execute(&block) }.to yield_with_args(target_commit.id)
+        end
+      end
+
+      context 'and target ref does not exist in source repo' do
+        let_it_be(:target_project) { create(:project, :repository) }
+
+        it 'fetches from the target to a temporary ref' do
+          new_commit_id = create_commit(target_project.owner, target_repo, target_branch)
+
+          # This is how the temporary ref is generated
+          expect(SecureRandom).to receive(:hex).at_least(:once).and_return('foo')
+
+          expect(source_repo)
+            .to receive(:fetch_source_branch!)
+            .with(target_repo, new_commit_id, 'refs/tmp/foo')
+            .and_call_original
+
+          expect(source_repo).to receive(:delete_refs).with('refs/tmp/foo').and_call_original
+
+          expect { |block| execute(&block) }.to yield_with_args(new_commit_id)
+        end
+      end
+
+      context 'and target ref does not exist in target repo' do
+        let(:target_branch) { 'does-not-exist' }
+
+        it 'returns nil' do
+          expect(source_repo).not_to receive(:fetch_source_branch!)
+          expect(source_repo).not_to receive(:delete_refs)
+
+          expect { |block| execute(&block) }.not_to yield_control
+        end
+      end
+    end
+  end
+
+  def create_commit(user, repo, branch)
+    action = { action: :create, file_path: '/FILE', content: 'content' }
+
+    result = repo.commit_files(user, branch_name: branch, message: 'Commit', actions: [action])
+
+    result.newrev
+  end
+end