My lawn has not been as green and lush as it was in the past which is why I joined this forum. In fact some areas are very brown and probably dead.

I live in Sacramento and have fescue/kbg blend.

I've learned a lot and have already been applying some of the advice:
Water deep and infrequent
Mulch mowing
Mow high
Fertilize with alfalfa, and occasionally some used coffee grounds.
I applied around 6oz of shampoo to my 2000 sq ft of lawn.

I made a mistake and shocked my lawn by switching to weekly waterings when it was used to every other day.

I plan to amend my soil with OM in the fall, plus overseed entire lawn.

Is a soil test critical now? Or can it wait or do I even need one at all?

Thanks for the help.