Get the `merge-base` of 2 refs trough the API

This adds an endpoint to get the common ancestor of 2 refs from the API.

1 files changed, 95 insertions, 0 deletions

diff --git a/spec/lib/gitlab/git/merge_base_spec.rb b/spec/lib/gitlab/git/merge_base_spec.rb
new file mode 100644
index 00000000000..2f4e043a20f
--- /dev/null
+++ b/spec/lib/gitlab/git/merge_base_spec.rb
@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Git::MergeBase do
+  set(:project) { create(:project, :repository) }
+  let(:repository) { project.repository }
+  subject(:merge_base) { described_class.new(repository, refs) }
+
+  shared_context 'existing refs with a merge base', :existing_refs do
+    let(:refs) do
+      %w(304d257dcb821665ab5110318fc58a007bd104ed 0031876facac3f2b2702a0e53a26e89939a42209)
+    end
+  end
+
+  shared_context 'when passing a missing ref', :missing_ref do
+    let(:refs) do
+      %w(304d257dcb821665ab5110318fc58a007bd104ed aaaa)
+    end
+  end
+
+  shared_context 'when passing refs that do not have a common ancestor', :no_common_ancestor do
+    let(:refs) { ['304d257dcb821665ab5110318fc58a007bd104ed', TestEnv::BRANCH_SHA['orphaned-branch']] }
+  end
+
+  describe '#sha' do
+    context 'when the refs exist', :existing_refs do
+      it 'returns the SHA of the merge base' do
+        expect(merge_base.sha).not_to be_nil
+      end
+
+      it 'memoizes the result' do
+        expect(repository).to receive(:merge_base).once.and_call_original
+
+        2.times { merge_base.sha }
+      end
+    end
+
+    context 'when passing a missing ref', :missing_ref do
+      it 'does not call merge_base on the repository but raises an error' do
+        expect(repository).not_to receive(:merge_base)
+
+        expect { merge_base.sha }.to raise_error(Gitlab::Git::UnknownRef)
+      end
+    end
+
+    it 'returns `nil` when the refs do not have a common ancestor', :no_common_ancestor do
+      expect(merge_base.sha).to be_nil
+    end
+
+    it 'returns a merge base when passing 2 branch names' do
+      merge_base = described_class.new(repository, %w(master feature))
+
+      expect(merge_base.sha).to be_present
+    end
+
+    it 'returns a merge base when passing a tag name' do
+      merge_base = described_class.new(repository, %w(master v1.0.0))
+
+      expect(merge_base.sha).to be_present
+    end
+  end
+
+  describe '#commit' do
+    context 'for existing refs with a merge base', :existing_refs  do
+      it 'finds the commit for the merge base' do
+        expect(merge_base.commit).to be_a(Commit)
+      end
+
+      it 'only looks up the commit once' do
+        expect(repository).to receive(:commit_by).once.and_call_original
+
+        2.times { merge_base.commit }
+      end
+    end
+
+    it 'does not try to find the commit when there is no sha', :no_common_ancestor do
+      expect(repository).not_to receive(:commit_by)
+
+      merge_base.commit
+    end
+  end
+
+  describe '#unknown_refs', :missing_ref do
+    it 'returns the the refs passed that are not part of the repository' do
+      expect(merge_base.unknown_refs).to contain_exactly('aaaa')
+    end
+
+    it 'only looks up the commits once' do
+      expect(merge_base).to receive(:commits_for_refs).once.and_call_original
+
+      2.times { merge_base.unknown_refs }
+    end
+  end
+end