the only way to test an ECU is to change yours for a known working unit and see what happens 
Not really a practical diagnostic step to take, especially as it may be paired with immobiliers, etc. as the Omega's is.

Let's take another approach. What evidence do we have that the ECU has failed? No fuel pressure. Hardly conclusive.
The first thing I would have done is to check for power at the fuel pump. I'd only suspect the fuel pump if the power was there but no fuel pressure, in which case the new fuel pump would have resolved it.
So, perhaps we have no power to the fuel pump. Is there power to the fuel pump relay, is the fuse intact, if the relay is operated manually does the fuel pump run?
Let's say we have no ECU output to switch on the fuel pump. Does the ECU have power? Are there any stored codes? Is the crank sensor working? Is the immobiliser happy? Are there pulses to the fuel injectors and coil packs when cranking?
I simply can't see how you can replace a battery, alternator and fuel pump and still be up a blind alley, unless you are changing things at random rather than following proper diagnostic procedures that anyone charging the public for their services should be competent at. On that basis, would I allow them to change any more components, or even lift the bonnet again? Nope.
