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A GSpreadsheetDataProvider adapter doctest
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Import the class.

    >>> from quintagroup.gdocs.spreadsheet.content.gspreadsheet import GSpreadsheet

Create object

    >>> my_context = GSpreadsheet('id')

Get adapter

    >>> from quintagroup.gdocs.spreadsheet.interfaces import IGSpreadsheetDataProvider
    >>> adapter = IGSpreadsheetDataProvider(my_context)

Testing methods of adapter

    >>> wci = adapter.getWorksheetColumnsInfo()
    >>> wci
    ['col1', 'col2', 'col3', 'col4', 'col5']
    >>> feed = adapter.getListFeed()
    >>> len(feed.entry)
    5
    >>> keys = feed.entry[0].custom.keys()
    >>> keys.sort()
    >>> keys
    ['col1', 'col2', 'col3', 'col4', 'col5']
    >>> [feed.entry[0].custom[key].text for key in keys]
    ['11', '12', '13', '14', '15']