Web 2.0 has made it so fractured that massive communities exist on /r/EmuDev, Emulator 101 is a well known source for new learners, nesdev.org is the reference

Web 2.0 has made it so fractured that massive communities exist on /r/EmuDev, Emulator 101 is a well known source for new learners, nesdev.org is the reference for NES stuff, a shitton of the data we have is from the Web 1.0 days and is just as fractured, and we even have repos like https://github.com/marethyu/awesome-emu-resources https://github.com/marethyu/awesome-emu-resources that collect a shitload of useful stuff (including the test ROMs that other commenters have mentioned, that will only work if you perfectly emulate the target system). As well as that, many people are decapping entire chips and games, just for exact emulation. So, no, you're talking out your ass, sorry.