[is0tope]

Not a founder, but a serial side-project'er. Initial prototype typically has no tests, at least for the bits that are wired. Specific bits of complexity will have unit tests. At some stage might add integration tests using something like docker compose.

Use TDD for bits that have very limited scope and function. For instance, an order book class or similar. Otherwise code first, test bugs if needed. For smaller projects (that aren't critical espc.) overtesting can kill your momentum and motivation, which is an often overlooked resource.