Fix pull request compare link (#1832)

* Fix pull request compare link

* Integration test

integrations/pull_compare_test.go

@@ -0,0 +1,31 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package integrations
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPullCompare(t *testing.T) {
+	prepareTestEnv(t)
+
+	session := loginUser(t, "user2", "password")
+	req, err := http.NewRequest("GET", "/user2/repo1/pulls", nil)
+	assert.NoError(t, err)
+	resp := session.MakeRequest(t, req)
+	assert.EqualValues(t, http.StatusOK, resp.HeaderCode)
+	htmlDoc, err := NewHtmlParser(resp.Body)
+	assert.NoError(t, err)
+	link, exists := htmlDoc.doc.Find(".navbar").Find(".ui.green.button").Attr("href")
+	assert.True(t, exists, "The template has changed")
+
+	req, err = http.NewRequest("GET", link, nil)
+	assert.NoError(t, err)
+	resp = session.MakeRequest(t, req)
+	assert.EqualValues(t, http.StatusOK, resp.HeaderCode)
+}