The oracle approach mentioned downthread is what makes this practical even without conformance test suites. Run the original, capture input/output pairs, use those as your tests. Property-based testing tools like Hypothesis can generate thousands of edge cases automatically.

For solo devs this changes the calculus entirely. Supporting multiple languages used to mean maintaining multiple codebases - now you can treat the original as canonical and regenerate ports as needed. The test suite becomes the actual artifact you maintain.