def split_on_first_appearance(input_string, separator):
    """
    >>> split_on_first_appearance('test','/')
    'test'
    >>> split_on_first_appearance('test/','/')
    'test'
    >>> split_on_first_appearance('test/something','/')
    'test'
    """
    result = input_string.split(separator, 1)[0]
    return result
