def METHOD_NAME():
    """Returns install directory.
    When running tests in the install tree, the current working directory
    needs to be changed (e.g. to '/' to avoid finding artifacts from the
    build tree when testing the installation). The caveat is that Python
    scripts that run install tests may need to know the install directory.
    `os.environ['TEST_TMPDIR']` is the absolute path to a private writable
    directory. This function returns the path to this writable folder appended
    with 'installation'. This allows to use this writable folder to create
    additional files without modifying the install tree.
    """
    return os.path.join(os.environ['TEST_TMPDIR'], 'installation')