How to use the pglast.parse_plpgsql function in pglast

with pytest.raises(Error) as exc:
        parse_sql('FooBar')
    assert exc.typename == 'ParseError'
    assert exc.value.location == 1
    assert 'syntax error ' in str(exc.value)

    with pytest.raises(Error) as exc:
        parse_sql('SELECT foo FRON bar')
    assert exc.typename == 'ParseError'
    assert exc.value.location == 17
    errmsg = str(exc.value)
    assert 'syntax error at or near "bar"' in errmsg
    assert 'location 17' in errmsg

    with pytest.raises(Error) as exc:
        parse_plpgsql('CREATE FUMCTION add (a integer, b integer)'
                      ' RETURNS integer AS $$ BEGIN RETURN a + b; END; $$'
                      ' LANGUAGE plpgsql')
    assert exc.typename == 'ParseError'
    assert exc.value.location == 8
    errmsg = str(exc.value)
    assert 'syntax error at or near "FUMCTION"' in errmsg
    assert 'location 8' in errmsg

def test_basic():
    ptree = parse_sql('SELECT 1')
    assert isinstance(ptree, list)
    assert len(ptree) == 1
    rawstmt = ptree[0]
    assert isinstance(rawstmt, dict)
    assert rawstmt.keys() == {'RawStmt'}

    ptree = parse_plpgsql('CREATE FUNCTION add (a integer, b integer)'
                          ' RETURNS integer AS $$ BEGIN RETURN a + b; END; $$'
                          ' LANGUAGE plpgsql')
    assert len(ptree) == 1
    function = ptree[0]
    assert isinstance(function, dict)
    assert function.keys() == {'PLpgSQL_function'}

def workhorse(args):
    input = args.infile or sys.stdin
    with input:
        statement = input.read()

    if args.parse_tree or args.plpgsql:
        tree = parse_plpgsql(statement) if args.plpgsql else parse_sql(statement)
        if args.no_location:
            _remove_stmt_len_and_location(tree)
        output = args.outfile or sys.stdout
        with output:
            json.dump(tree, output, sort_keys=True, indent=2)
            output.write('\n')
    else:
        try:
            prettified = prettify(
                statement,
                compact_lists_margin=args.compact_lists_margin,
                split_string_literals_threshold=args.split_string_literals,
                special_functions=args.special_functions,
                comma_at_eoln=args.comma_at_eoln,
                semicolon_after_last_statement=args.semicolon_after_last_statement)
        except Error as e: