def test_multi_replace():
    course_source = '"/course/file.png"'

    assert replace_static_urls(STATIC_SOURCE, DATA_DIRECTORY) == \
        replace_static_urls(replace_static_urls(STATIC_SOURCE, DATA_DIRECTORY), DATA_DIRECTORY)
    assert replace_course_urls(course_source, COURSE_KEY) == \
        replace_course_urls(replace_course_urls(course_source, COURSE_KEY), COURSE_KEY)

def test_multi_replace():
    course_source = '"/course/file.png"'

    assert_equals(
        replace_static_urls(STATIC_SOURCE, DATA_DIRECTORY),
        replace_static_urls(replace_static_urls(STATIC_SOURCE, DATA_DIRECTORY), DATA_DIRECTORY)
    )
    assert_equals(
        replace_course_urls(course_source, course_id),
        replace_course_urls(replace_course_urls(course_source, course_id), course_id)
    )

def replace_course_urls(course_id, block, view, frag, context):  # pylint: disable=unused-argument
    """
    Updates the supplied module with a new get_html function that wraps
    the old get_html function and substitutes urls of the form /course/...
    with urls that are /courses/<course_id>/...
    """
    return wrap_fragment(frag, static_replace.replace_course_urls(frag.content, course_id))

 def _get_html():
     return static_replace.replace_course_urls(get_html(), course_id)