Python doctest file to simulate a WPS Execute invocation with INVALID arguments.
This test does not execute any live HTTP request, rather it parses XML files containing pre-made HTTP responses.

Imports

    >>> from __future__ import (absolute_import, division, print_function)
    >>> from tests.utils import resource_file, setup_logging
    >>> from owslib.wps import WebProcessingService
    >>> logger = setup_logging('INFO')

Initialize WPS client

    >>> wps = WebProcessingService('http://cida.usgs.gov/gdp/process/WebProcessingService')

Submit fake invocation of Execute operation using cached HTTP request and response
    >>> request = open(resource_file('wps_USGSExecuteInvalidRequest.xml'), 'rb').read()
    >>> response = open(resource_file('wps_USGSExecuteInvalidRequestResponse.xml'), 'rb').read()
    >>> execution = wps.execute(None, [], request=request, response=response)
    Executing WPS request...
    Execution status=ProcessFailed
    Percent completed=0
    Status message=None
     owslib.wps.WPSException : ...

    >>> execution.isComplete()
    True

Display errors
    >>> for ex in execution.errors:
    ...     ex.code, ex.locator, ex.text
    ... 
    (None, None, 'Attribute null not found in feature collection')
