add yank-pop test based on suggestion in PR zsh-users#551

spec/yank_pop_spec.rb

@@ -0,0 +1,18 @@
+context 'after positioning cursor before a word' do
+  before do
+    session.send_string('echo hello world bye')
+  end
+
+  describe '`yank` then `yank-pop`' do
+    it 'should insert text in correct position before word' do
+      session.send_keys('C-w').send_keys('C-h').send_keys('C-w')
+      wait_for { session.content }.to eq('echo hello')
+
+      session.send_keys('M-b').send_keys('C-y')
+      wait_for { session.content }.to eq('echo worldhello')
+
+      session.send_keys('M-y')
+      wait_for { session.content }.to eq('echo byehello')
+    end
+  end
+end