Add spec for GitLab.com importer

spec/lib/gitlab/gitlab_import/importer_spec.rb

+require 'spec_helper'
+
+describe Gitlab::GitlabImport::Importer, lib: true do
+  describe '#execute' do
+    it 'persists issues' do
+      stub_request('issues', [
+        {
+          'id' => 2579857,
+          'iid' => 3,
+          'title' => 'Issue',
+          'description' => 'Lorem ipsum',
+          'state' => 'opened',
+          'author' => {
+            'id' => 283999,
+            'name' => 'John Doe'
+          }
+        }
+      ])
+      stub_request('issues/2579857/notes', [])
+
+      project = create(:empty_project, import_source: 'asd/vim')
+      project.build_import_data(credentials: { password: 'password' })
+
+      subject = described_class.new(project)
+      subject.execute
+
+      expected_attributes = {
+        iid: 3,
+        title: 'Issue',
+        description: "*Created by: John Doe*\n\nLorem ipsum",
+        state: 'opened',
+        author_id: project.creator_id
+      }
+
+      expect(project.issues.first).to have_attributes(expected_attributes)
+    end
+
+    def stub_request(path, body)
+      url = "https://gitlab.com/api/v3/projects/asd%2Fvim/#{path}?page=1&per_page=100"
+
+      WebMock.stub_request(:get, url).
+        to_return(
+          headers: { 'Content-Type' => 'application/json' },
+          body: body
+        )
+    end
+  end
+end