This sounds like a good idea. I am developing a custom MPC8349E board that I'll submit a U-Boot patch for when its done. I also plan to build a test-suite that executes as a u-boot stand-alone application. Its not clear to me that such a test suite should also be added into the U-Boot source, since its board-specific; more so than whatever changes to the current MPC8349E support I need to get the board booted. Although, I have no intention of hiding the test-suite source code.
You can put it in the board folder and have a separate make rule to choose when to compile it. In my case, though, the diagnostic tests never reach a finished state and really are only for our produtction testing.
I figured I'd submit the board support patch, and then just maintain the test-suite locally, with an email reference in a u-boot README to anyone who wanted to get access to the test-suite code. Of course, if lots of people build test suites using U-Boot, and there is common code, I'd be happy to use it. I just haven't looked for it in the source yet. The test suite would involve programming Altera FPGAs with FPGA configurations, running pin-to-pin tests, etc.
So is this the intention of your proposal, or just another use-case your proposal would support?
Actually, that is almost my exact intention.
You'll see in an e-mailed patch to this list earlier this week (I think, maybe it was last week), I started adding finctions to the exports function. I'd like to better document the stand alone programs feature. Also if there is intrest and if I have time, I'll look at putting together a barebone test suite starter package with instructions.