poseidon: Add circuit test case that fails

This exposes a bug in the way padding was being handled by the invalid
sponge-duplex hybrid construction.

src/circuit/gadget/poseidon/pow5.rs

@@ -823,6 +823,22 @@ mod tests {
         assert_eq!(prover.verify(), Ok(()))
     }
 
+    #[test]
+    fn poseidon_hash_longer_input() {
+        let message = [Fp::rand(), Fp::rand(), Fp::rand()];
+        let output =
+            poseidon::Hash::<_, OrchardNullifier, ConstantLength<3>, 3, 2>::init().hash(message);
+
+        let k = 7;
+        let circuit = HashCircuit::<OrchardNullifier, 3, 2, 3> {
+            message: Some(message),
+            output: Some(output),
+            _spec: PhantomData,
+        };
+        let prover = MockProver::run(k, &circuit, vec![]).unwrap();
+        assert_eq!(prover.verify(), Ok(()))
+    }
+
     #[test]
     fn hash_test_vectors() {
         for tv in crate::primitives::poseidon::test_vectors::fp::hash() {