- Their language runtime supported thread-based concurrency, which would drastically reduce implementation complexity and actual per-task overhead, thus improving machine usage efficiency AND eliminating the concerns about managing process trees that introduces a requirement for things like Docker.
- Their language runtime was AOT or JIT compiled, simply making everything faster to a degree that test execution could be reasonably performed on one (potentially large) machine.
- They used a language with a decent type system, significantly reducing the number of tests that had to be both written and run?