Issue while importing variable from one file to other

[Larz60+]

the third line of this sequence is the culprit:

    def __init__(self, child):
        Tkinter.Frame.__init__(self, child)
        autotest = Testing.TestingPage()

The first error message doesn't seem to be complete. Did you post the whole error?
There should be more that explains what the issue is.
somewhere in the __init__ method of AutomationTestingPage_ITOM class you need to define ser
(self.ser = whatever)
then when referencing ser in other methods use self.ser
example in data_tx method,

def data_tx(self):
        element = [0x4D, 0x08, 0xFF, 0x06, 0x1A, 0x52]
        data = bytearray(element)
        self.ser.write(data)
        receivedata = (self.ser.read(7))
        data1 = binascii.b2a_hex(receivedata)
        data2 = ord(receivedata[6])
        return data2