I have a ceiling light in the hallway with two light switches (dipoles?). The
ceiling light has 4 bulbs. The other day the hallway light wouldn't turn on
with known good bulbs.

Not knowing anything about electricity I *assumed* that one of the switches
had to be defective so I replaced both on/off switches -- that didn't solve
the problem.

There's electricity in both boxes to other lamps so I know (think) that it's
not a circuit breaker problem.

Before proceeding any further (e.g. replace the lamp fixture), I bought a
simple current tester to see if there's any electricity in either of the
light switches.

Not knowing what/how to test, I put the test probes on each of the wires for
both switches in every conceivable configuration. The diode never glowed.

Beside laying out a few hundred dollars for an electrician to deign making
his royal appearance, what can I do first to resolve this problem?