(This question was inspired by my previous question What kind of software was used to develop Nintendo 64 titles?)
The NES used a modified 6502 processor and most games were written in Assembly. There are a number of open source tools available for writing, compiling, and decompiling NES executables, but what was Nintendo's official development environment like? What was the process of writing the assembly, compiling it, testing (locally?), and building test cartridges? What hardware was used for development? Were dev kits and environments given to select third parties for development? If not, what resources did third-party developers use?