h5Driver.isElementExist根据xpath获取元素，xpath expression 无效导致异常，api返回查找元素结果为True

[lan-tianyu]

代码部分，如下has_all_tab_cur 结果为true，实际看了日志才发现其实是没有找到元素的。

all_tab_xpath` = './/*[text()="所有订单"'
has_all_tab_cur = h5Driver.isElementExist(all_tab_xpath)

C:\Python27\Lib\site-packages\fastAutoTest\core\h5\h5Engine.py 方法 isElementExist 增加resultValueDict = self._networkHandler.send(getExistCmd).getResponse()[0]结果打印

        resultValueDict = self._networkHandler.send(getExistCmd).getResponse()[0]
        self.logger.debug("resultValueDict: {resultValueDict}".format(resultValueDict=resultValueDict))
        resultType = resultValueDict['result']['result']['subtype']
        num = 0
        while resultType == 'null' and num < 3:
            self.wait(WAIT_REFLESH_2_SECOND)
            getExistCmd = self._pageOperator.isElementExist(xpath, contextId)
            resultValueDict = self._networkHandler.send(getExistCmd).getResponse()[0]
            resultType = resultValueDict['result']['result']['subtype']
            num = num + 1
        return resultType != 'null'

日志：

[2018-11-02 18:21:12,907] [pid:5688] [h5Engine.py:478] [isElementExist] DEBUG: resultValueDict: {u'result': {u'exceptionDetails': {u'columnNumber': 53, u'exception': {u'className': u'DOMException', u'subtype': u'error', u'type': u'object', u'description': u'DOMException: Failed to execute \'evaluate\' on \'Document\': The string \'.//*[text()="\u6240\u6709\u8ba2\u5355"\' is not a valid XPath expression.\n    at <anonymous>:1:54', u'objectId': u'{"injectedScriptId":7,"id":2}'}, u'text': u'Uncaught', u'exceptionId': 1, u'scriptId': u'317', u'lineNumber': 0}, u'result': {u'className': u'DOMException', u'subtype': u'error', u'type': u'object', u'description': u'DOMException: Failed to execute \'evaluate\' on \'Document\': The string \'.//*[text()="\u6240\u6709\u8ba2\u5355"\' is not a valid XPath expression.\n    at <anonymous>:1:54', u'objectId': u'{"injectedScriptId":7,"id":1}'}}}
True

分析：
resultValueDict 返回结果的json数据如下，其中 resultValueDict['result']['result']['subtype']值为‘error’。源码中只判断了resultType != 'null'，导致返回结果为true。使用者在未打开日志的场景下，并不知道自己的xpath expression 是错误的，还以为是找到了元素，这对结果的判断是不准确的。

{
	u 'result': {
		u 'exceptionDetails': {
			u 'columnNumber': 53,
			u 'exception': {
				u 'className': u 'DOMException',
				u 'subtype': u 'error',
				u 'type': u 'object',
				u 'description': u 'DOMException: Failed to execute \'evaluate\' on \'Document\': The string \'.//*[text()="\u6240\u6709\u8ba2\u5355"\' is not a valid XPath expression.\n    at <anonymous>:1:54',
				u 'objectId': u '{"injectedScriptId":7,"id":2}'
			},
			u 'text': u 'Uncaught',
			u 'exceptionId': 1,
			u 'scriptId': u '317',
			u 'lineNumber': 0
		},
		u 'result': {
			u 'className': u 'DOMException',
			u 'subtype': u 'error',
			u 'type': u 'object',
			u 'description': u 'DOMException: Failed to execute \'evaluate\' on \'Document\': The string \'.//*[text()="\u6240\u6709\u8ba2\u5355"\' is not a valid XPath expression.\n    at <anonymous>:1:54',
			u 'objectId': u '{"injectedScriptId":7,"id":1}'
		}
	}
}