<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def raises_gathered(error_type):
    '''For use in tests. Many tests expect a single error to be thrown, and
    want it to be of a specific type. This is a helper method for when that
    type is inside a gathered exception.'''
    container = RaisesGatheredContainer()
    try:
        yield container
    except GatheredExceptions as e:
        # Make sure there is exactly one exception.
        if len(e.exceptions) != 1:
            raise
        inner = e.exceptions[0]
        # Make sure the exception is the right type.
        if not isinstance(inner, error_type):
            raise
        # Success.
        container.exception = inner