[specs] add test case for job MembershipWarningJob

spec/jobs/membership_warning_job.rb

@@ -0,0 +1,15 @@
+RSpec.describe MembershipWarningJob, type: :job do
+  let!(:org) { Fabricate(:organization) }
+  let!(:user) { Fabricate(:user) }
+  let!(:member) { Fabricate(:member, organization: org, user: user) }
+  let!(:user_with_no_memberships) { Fabricate(:user) }
+  let!(:user_with_no_memberships2) { Fabricate(:user, created_at: 16.days.ago) }
+
+  describe '#perform' do
+    it "should send emails in user's locale" do
+      expect {
+        MembershipWarningJob.perform_now
+      }.to change { ActionMailer::Base.deliveries.count }.by(1)
+    end
+  end
+end