Metamorphic Test Generator

Normal test: "for input X, output should be Y." But what if you don't know Y? Metamorphic test: "for inputs X and X', the outputs should relate in a known way." You don't need an oracle — you need a metamorphic relation.

The core idea

         f
  X ─────────► Y           You don't know Y.
  │            │
  │ transform  │ relation  But you know: if X' = transform(X),
  ▼            ▼           then f(X') should relate to f(X).
  X' ────────► Y'
         f

If the relation fails, f is wrong. You found a bug without knowing the right answer.

Metamorphic relation catalog