Add failing test-case

tests/prover.rs

@@ -0,0 +1,72 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// Copyright (c) DUSK NETWORK. All rights reserved.
+
+use dusk_plonk::prelude::*;
+use rand::rngs::StdRng;
+use rand::SeedableRng;
+
+const CAPACITY: usize = 1 << 4;
+const LABEL: &[u8] = b"check_public_inputs";
+
+#[derive(Default)]
+pub struct TestPI {
+    public: Vec<BlsScalar>,
+    sum: BlsScalar,
+}
+
+impl TestPI {
+    pub fn new(public: Vec<BlsScalar>, sum: BlsScalar) -> Self {
+        Self { public, sum }
+    }
+}
+
+impl Circuit for TestPI {
+    fn circuit(&self, composer: &mut Composer) -> Result<(), Error> {
+        // this circuit will always have the same amount of gates but different
+        // amount of public inputs, depending on the struct data
+        let mut sum = Composer::ZERO;
+        for i in 0..2 {
+            let constraint = match i < self.public.len() {
+                true => Constraint::new()
+                    .left(1)
+                    .a(sum)
+                    .right(1)
+                    .b(Composer::ONE)
+                    .public(self.public[i]),
+                false => {
+                    Constraint::new().left(1).a(sum).right(1).b(Composer::ONE)
+                }
+            };
+            sum = composer.gate_add(constraint);
+        }
+        let expected_sum = composer.append_witness(self.sum);
+        composer.assert_equal(sum, expected_sum);
+
+        Ok(())
+    }
+}
+
+#[test]
+fn public_inputs() {
+    let rng = &mut StdRng::seed_from_u64(0x10b);
+    let pp = PublicParameters::setup(CAPACITY, rng)
+        .expect("Creation of public parameter shouldn't fail");
+
+    // compiling the default version of TestPI, which has no pi
+    let (prover, _verifier) = Compiler::compile::<TestPI>(&pp, LABEL)
+        .expect("It should be possible to compile the prover and verifier");
+
+    // Create circuit with public inputs
+    let pi: Vec<BlsScalar> = [BlsScalar::one(); 2].into();
+    let sum = BlsScalar::from(4);
+    let circuit = TestPI::new(pi, sum);
+    let result = prover.prove(rng, &circuit);
+    assert_eq!(
+        result.unwrap_err(),
+        Error::PublicInputNotFound { index: 0 },
+        "proof creation for different sized circuit shouldn't be possible"
+    );
+}