Add a range demo test

tests/range.rs

@@ -0,0 +1,35 @@
+#![allow(non_snake_case)]
+use curve25519_dalek::ristretto::RistrettoPoint as G;
+use group::ff::PrimeField;
+use group::Group;
+use sha2::Sha512;
+use sigma_compiler::*;
+
+#[test]
+fn range_test() -> Result<(), sigma_rs::errors::Error> {
+    sigma_compiler! { proof,
+        (x, y, pub a, rand r),
+        (C, D, const cind A, const cind B),
+        C = (3*x+1)*A + (2*r+3)*B,
+        D = x*A + y*B,
+        (a..20).contains(x),
+        (0..a).contains(y),
+    }
+
+    type Scalar = <G as Group>::Scalar;
+    let mut rng = rand::thread_rng();
+    let A = G::hash_from_bytes::<Sha512>(b"Generator A");
+    let B = G::generator();
+    let a = Scalar::from_u128(3);
+    let r = Scalar::random(&mut rng);
+    let x = Scalar::from_u128(19);
+    let y = Scalar::from_u128(2);
+    let C = (x + x + x + Scalar::ONE) * A + (r + r + Scalar::from_u128(3)) * B;
+    let D = x * A + y * B;
+
+    let params = proof::Params { C, D, a, A, B };
+    let witness = proof::Witness { x, y, r };
+
+    let proof = proof::prove(&params, &witness, &mut rng)?;
+    proof::verify(&params, &proof)
+}