This codepath is only used when inspecting a transaction that does not involve the wallet. So open any wallet, go to a block explorer and copy the rax hex data for a random transaction, use the `Tools > Load Transaction > From Text` menu and paste the raw hex. Check that the dialog shows the correct block height for this tx.
If running Electrum ABC in verbose mode, look out for the "fetch_input_data: got tx block height" message