Since Node is being built by a community fully committed to code sharing, where interoperability between modules is so important, it should come as no surprise that code testing tools and frameworks entered Node's ecosystem right after inception. Indeed, the normally parsimonious core Node team added the assert module early on, suggesting a recognition that testing is a fundamental part of the development process.
Testing is not solely a bug-detecting and defect-fixing process. Test-Driven Development, for example, insists on having tests precede the existence of any code! Testing, generally, is the process of making comparisons between the existing behavior and desired behavior in software, where new information is continuously fed back into the process...