There are quite a number of test suites for the 6502 processors, such as those by Klaus Dormann and Rob Finch.

I'm looking for similar test suites for the Motorola MC6800 CPU. Has anybody got any pointers for me? Even if they're incomplete, I'd be interested in hearing about them. Failing that, are there some pieces of pure code (i.e., not needing to do I/O or relying on other devices in the system beyond memory) that would reasonably exercise the basic instruction set and flag possible errors?

Anything here of any use?
http://test.dankohn.info/~myhome/projects/68HC11/AXIOM_HC11/Source/Users%20Group/index.txt
http://test.dankohn.info/~myhome/projects/68HC11/AXIOM_HC11/Source/Users%20Group/

An excellent request! Unfortunately, I don't have any pointers. I think I must have looked, when we were bringing up the visual6800.
http://visual6502.org/JSSim/expert-6800.html

Oh, that looks good to me!

12 MPU INSTRUCTION TEST

Yes, the "MPU Instruction Test" looks very hopeful, and it also looks as if there are some other routines there that should have fairly easily testable results. Thanks!