Improve specs for Repositories API

changelogs/unreleased/4269-public-repositories-api.yml

 ---
 title: Allow Repositories API GET endpoints to be requested anonymously
-merge_request:
+merge_request: 8148
 author:

spec/support/api/status_shared_examples.rb

+# Specs for status checking.
+#
+# Requires an API request:
+#   let(:request) { get api("/projects/#{project.id}/repository/branches", user) }
+shared_examples_for '400 response' do
+  before do
+    # Fires the request
+    request
+  end
+
+  it 'returns 400' do
+    expect(response).to have_http_status(400)
+  end
+end
+
+shared_examples_for '403 response' do
+  before do
+    # Fires the request
+    request
+  end
+
+  it 'returns 403' do
+    expect(response).to have_http_status(403)
+  end
+end
+
+shared_examples_for '404 response' do
+  let(:message) { nil }
+  before do
+    # Fires the request
+    request
+  end
+
+  it 'returns 404' do
+    expect(response).to have_http_status(404)
+    expect(json_response).to be_an Object
+
+    if message.present?
+      expect(json_response['message']).to eq(message)
+    end
+  end
+end