There are a number of test suites for 6502, each with their own intentions and peculiarities.
For the most part they aim to test emulators, which are subject to different bugs than CPU implementations, and therefore the effective coverage may not be as good as expected. Such tests are generally self-checking - there is no golden results file of bus activity - and generally assume some specific platform's I/O facilities.
Self-testing (6502 ROMs and programs):
- Wolfgang Lorenz' C64 suite exhaustive, excluding decimal mode, uses C64 facilities to chain each program (stubbing instructions here by Christer Palm) (testsuite on Tom Seddon's site) (11kbyte total) (some description)
- Ruud Baltissen's 8k test ROM from his VHDL 6502 core (includes source, presently off-air)
- NES test rom by Kevin Horton (24kbyte) (haven't found source for this, he says he hasn't got clean source to release)
- AllSuiteA.asm from the hcm-6502 (verilog) project. ROM available.
- Decimal mode tests by Bruce Clark ADC/SBC
- Test code supplied with Rob Finch's 6502 core (archive.org) (1500 bytes)
- py65 tests by Mike Naberezny (python)