One company's SOP...
b744FPEK,
A couple of points:
1. Don't transmit on HF during refueling.
2. Not a good idea to transmit on HF when ground personnel are close by.
3. To test, use an LDOC frequency. (One that is not necessarily used for ATC.) For example, a company frequency, or an ARINC frequency that is used for company traffic...phone patches, etc. If unavailable, then use a frequency that works.
Tune both HFs to the same frequency (as selected above). Hit the mic for a moment to get the auto-tune going. (Do this for each HF.)
Call your station on HF1. Wait for reply.
When reply is received, go to HF2 and ask for a SELCAL check. Give your SELCAL code.
Wait for SELCAL on each/both HF receivers.
This method tests the transmitters for both HFs, the receivers for both HFs, and the SELCAL function for both HFs.
Fly safe,
PantLoad