Escape CSS IDs correctly for SoupSieve

Fixes an instance of #61 in getLink().

CHANGES.rst

@@ -8,6 +8,10 @@ CHANGES
 - Fix a bug where clicking the selected radio button would unselect it.  See
   `issue 68 <https://github.com/zopefoundation/zope.testbrowser/issues/68>`_.
 
+- Fix another incompatibility with BeautifulSoup4 >= 4.7 that could result
+  in a SyntaxError from browser.getLink().  See `issue 61
+  <https://github.com/zopefoundation/zope.testbrowser/issues/61>`_.
+
 
 5.3.2 (2019-02-06)
 ------------------

src/zope/testbrowser/browser.py

@@ -27,6 +27,7 @@
 from zope.cachedescriptors.property import Lazy
 from wsgiproxy.proxies import TransparentProxy
 from bs4 import BeautifulSoup
+from soupsieve import escape as css_escape
 
 from zope.testbrowser import interfaces
 from zope.testbrowser._compat import httpclient, PYTHON2
@@ -313,8 +314,8 @@ def _setResponse(self, response):
 
     def getLink(self, text=None, url=None, id=None, index=0):
         """See zope.testbrowser.interfaces.IBrowser"""
-        qa = 'a' if id is None else 'a#%s' % id
-        qarea = 'area' if id is None else 'area#%s' % id
+        qa = 'a' if id is None else 'a#%s' % css_escape(id)
+        qarea = 'area' if id is None else 'area#%s' % css_escape(id)
         html = self._html
         links = html.select(qa)
         links.extend(html.select(qarea))