def METHOD_NAME(output_dir):
    """Merges the kcov data of individual test runs into output_dir."""
    dirs = find_kcov_test_outputs()
    if not dirs:
        sys.exit("Error: no kcov data to merge")
    for d in dirs:
        maybe_expand_zipped_kcov_data(d)
    cmd = ['kcov', '--merge', output_dir]
    cmd.extend([os.path.join(d, 'kcov') for d in dirs])
    subprocess.run(cmd, check=True)