How to use the cfgrib.cfmessage.build_valid_time function in cfgrib

def test_build_valid_time():
    forecast_reference_time = np.array(0)
    forecast_period = np.array(0)

    dims, data = cfmessage.build_valid_time(forecast_reference_time, forecast_period)

    assert dims == ()
    assert data.shape == ()

    forecast_reference_time = np.array([0, 31536000])
    forecast_period = np.array(0)

    dims, data = cfmessage.build_valid_time(forecast_reference_time, forecast_period)

    assert dims == ('time',)
    assert data.shape == forecast_reference_time.shape + forecast_period.shape

    forecast_reference_time = np.array(0)
    forecast_period = np.array([0, 12, 24, 36])

    dims, data = cfmessage.build_valid_time(forecast_reference_time, forecast_period)

for dim in header_dimensions:
            header_value = header_values[index.index_keys.index(coord_name_key_map.get(dim, dim))]
            header_indexes.append(coord_vars[dim].data.tolist().index(header_value))
        offsets[tuple(header_indexes)] = offset
    missing_value = data_var_attrs.get('missingValue', 9999)
    data = OnDiskArray(
        stream=index.filestream,
        shape=shape,
        offsets=offsets,
        missing_value=missing_value,
        geo_ndim=len(geo_dims),
    )

    if 'time' in coord_vars and 'step' in coord_vars:
        # add the 'valid_time' secondary coordinate
        dims, time_data = cfmessage.build_valid_time(
            coord_vars['time'].data,
            coord_vars['step'].data,
        )
        attrs = COORD_ATTRS['valid_time']
        coord_vars['valid_time'] = Variable(dimensions=dims, data=time_data, attributes=attrs)

    data_var_attrs['coordinates'] = ' '.join(coord_vars.keys())
    data_var = Variable(dimensions=dimensions, data=data, attributes=data_var_attrs)
    dims = collections.OrderedDict((d, s) for d, s in zip(dimensions, data_var.data.shape))
    return dims, data_var, coord_vars