Pyhton Script Called by xlwings Addin

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I am attempting to use a basic example of xlwings. I have the following VBA script:

Sub Test()
        RunPython ("import VBAtester; VBAtester.test()")
        MsgBox ("Script has run.")
    End Sub

Which is in the same directory as the python script VBAtester.py:

import xlwings as xw
def test():
wb = xw.Book.caller()
wb.sheets[0].range('A1').value = 'TEST VALUE'


The VBA script runs and outputs the message box; but *'TEST VALUE'* does not show in cell A1, or elsewhere. I know the python script is being called as if I purposefully put errors in my python script VBA will callback these errors when I run the VBA script that calls the python script.

What is the error in my understanding or my approach?

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