def METHOD_NAME():
    """
    Test grains._linux_lvm, lvm is installed but no volume groups created.
    Should return a dictionary only with the header
    """
    vgs_out = {"pid": 123, "retcode": 0, "stdout": "", "stderr": ""}
    cmd_out = MagicMock(autospec=True, side_effect=[vgs_out])
    patch_which = patch(
        "salt.utils.path.which", autospec=True, return_value="/usr/sbin/lvm"
    )
    patch_cmd_lvm = patch.dict(lvm.__salt__, {"cmd.run_all": cmd_out})
    with patch_which, patch_cmd_lvm:
        ret = lvm._linux_lvm()
    assert ret == {"lvm": {}}, ret