真机上已经调用如下类方法进行了安装 app

class installApp():
    '''  安装app   '''
    def installAndroidApp(self):
        '''  定义安装app函数--安卓     '''
        # Returns abs path relative to this file and not cwd
        PATH = lambda p: os.path.abspath(os.path.join(os.path.dirname(__file__), p))

        desired_caps = {}
        desired_caps['platformName'] = 'Android'
        desired_caps['platformVersion'] = '4.3'
        desired_caps['deviceName'] = 'Android Emulator'
        desired_caps['app'] = PATH(r'G:\workspace\src\common\testApp\testApp.apk')
        desired_caps['app-Package'] = 'com.android.test'
        desired_caps['app-Activity'] = '.test'

        driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_caps)
        time.sleep(2)

        return driver

执行下一个用例的时候，也需要使用 driver 的属性方法，可是不能再调用上面的函数了，因为调用还是会再次安装 app，
请问：如何在不安装 app 的情况下，获取 driver 的属性方法呢？

查询了下资料，说是将

desired_caps['app'] = PATH(r'G:\workspace\src\common\testApp\testApp.apk')
代码注释掉，不过我试了，注释掉上面这行后，依然报错：

#!/usr/bin/env python
# -*- encoding:UTF-8 -*-

from appium import webdriver
import time,os

class getDriverInfo():
    '''    获取driver属性信息的类     '''

    def androidDriverInfo(self):
        '''   定义获取driver属性信息的函数--安卓     '''
        # Returns abs path relative to this file and not cwd
        #PATH = lambda p: os.path.abspath(os.path.join(os.path.dirname(__file__), p))

        desired_caps = {}
        desired_caps['platformName'] = 'Android'
        desired_caps['platformVersion'] = '4.3'
        desired_caps['deviceName'] = 'Android Emulator'
        #desired_caps['app'] = PATH(r'G:\workspace\src\common\testApp\testApp.apk')
        desired_caps['app-Package'] = 'com.android.test'
        desired_caps['app-Activity'] = '.test'

        driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_caps)
        time.sleep(2)
        return driver


if __name__ == '__main__':
    driverInfo = getDriverInfo()
    app = driverInfo.androidDriverInfo()
    print app.contexts()

报错的信息如下：
File "C:\Python27\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 164, in check_response
raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.WebDriverException: Message: u"A new session could not be created. (Original error: No app set; either start appium with --app or pass in an 'app' value in desired capabilities, or set androidPackage to launch pre-existing app on device)"

请问大家是如何解决执行测试用例的时候，不要每次都重新安装 apk ，就可以获取 driver 属性信息的？