diff --git a/spec/models/services/twitter_spec.rb b/spec/models/services/twitter_spec.rb
new file mode 100644
index 00000000..352ed369
--- /dev/null
+++ b/spec/models/services/twitter_spec.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Services::Twitter do
+  describe "#post" do
+    let(:user) { FactoryBot.create(:user) }
+    let(:service) { Services::Twitter.create(user: user) }
+    let(:answer) { FactoryBot.create(:answer, user: user,
+                                     content: 'a' * 255,
+                                     question_content: 'q' * 255) }
+    let(:twitter_client) { instance_double(Twitter::REST::Client) }
+
+    before do
+      allow(Twitter::REST::Client).to receive(:new).and_return(twitter_client)
+      allow(twitter_client).to receive(:update!)
+      stub_const("APP_CONFIG", {
+        'hostname' => 'example.com',
+        'https' => true,
+        'items_per_page' => 5,
+        'sharing' => {
+          'twitter' => {
+            'consumer_key' => 'AAA',
+          }
+        }
+      })
+    end
+
+    it "posts a shortened tweet" do
+      service.post(answer)
+
+      expect(twitter_client).to have_received(:update!).with("#{'q' * 123}… — #{'a' * 124}… https://example.com/#{user.screen_name}/a/#{answer.id}")
+    end
+  end
+end
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