test(logging): improve _log with single parameter with sinon.spy

test/unit/logging.html

@@ -88,17 +88,16 @@
   suite('_logger', () => {
     test('_log with single parameter', () => {
       const msg = 'log test';
-      const logHistory = [];
       const orgConsole = console;      
+      const spy = sinon.spy();
       window.console = {
-        log: msg => {
-          logHistory.push(msg);
-        }
+        log: spy
       };
       Polymer.Base._log(msg);
       window.console = orgConsole;
-      assert.equal(logHistory[0], msg);
-      assert.equal(logHistory.length, 1, 'console.log called more than one time');
+      assert.equal(spy.callCount, 1, 'console.log called more than one time');
+      assert.equal(spy.args[0].length, 1, 'console.log called with more than one argument');
+      assert.equal(spy.args[0][0], msg, 'message not pass properly to log');
     });
   });
   </script>