chore: add failing test for unsupported relation.

Author: mmaker

src/linear_relation/mod.rs

@@ -676,9 +676,7 @@ impl<G: PrimeGroup> TryFrom<&LinearRelation<G>> for CanonicalLinearRelation<G> {
             .image()
             .is_ok_and(|img| img.iter().all(|&x| x != G::identity()))
         {
-            return Err(InvalidInstance::new(
-                "Image contains identity element"
-            ));
+            return Err(InvalidInstance::new("Image contains identity element"));
         }
 
         // If any linear combination is empty, the relation is invalid
@@ -688,17 +686,17 @@ impl<G: PrimeGroup> TryFrom<&LinearRelation<G>> for CanonicalLinearRelation<G> {
             .iter()
             .any(|lc| lc.0.is_empty())
         {
-            return Err(InvalidInstance::new(
-                "Linear combinations cannot be empty",
-            ));
+            return Err(InvalidInstance::new("Linear combinations cannot be empty"));
         }
 
         // If any linear combination has no witness variables, the relation is invalid
         if relation.linear_map.linear_combinations.iter().any(|lc| {
             lc.0.iter()
                 .all(|weighted| matches!(weighted.term.scalar, ScalarTerm::Unit))
         }) {
-            return Err(InvalidInstance::new("A linear combination does not have any witness variables"));
+            return Err(InvalidInstance::new(
+                "A linear combination does not have any witness variables",
+            ));
         }
 
         let mut canonical = CanonicalLinearRelation::new();

src/tests/test_relations.rs

@@ -324,7 +324,6 @@ fn subtractions_with_shift<G: PrimeGroup, R: RngCore>(
     (instance, witness)
 }
 
-
 #[allow(non_snake_case)]
 fn cmz_wallet_spend_relation<G: PrimeGroup, R: RngCore>(
     mut rng: &mut R,
@@ -371,6 +370,34 @@ fn cmz_wallet_spend_relation<G: PrimeGroup, R: RngCore>(
     (instance, witness)
 }
 
+
+fn test_another_relation<G: PrimeGroup, R: RngCore>(
+    mut rng: &mut R,
+) -> (CanonicalLinearRelation<G>, Vec<G::Scalar>) {
+    let mut instance = LinearRelation::<G>::new();
+    let r = instance.allocate_scalar();
+    let var_A = instance.allocate_element();
+    let var_B = instance.allocate_element();
+    let eq1 = instance.allocate_eq(
+        var_A * G::Scalar::from(4)
+            + (r * G::Scalar::from(2) + G::Scalar::from(3)) * var_B,
+    );
+
+    let A = G::random(&mut rng);
+    let B = G::random(&mut rng);
+    let r = G::Scalar::random(&mut rng);
+    let C = A * G::Scalar::from(4)
+            + (r * G::Scalar::from(2) + G::Scalar::from(3)) * var_B;
+    instance.set_element(var_A, A);
+    instance.set_element(var_B, B);
+    instance.set_element(eq1, C);
+
+    let witness = vec![r];
+    let instance = CanonicalLinearRelation::try_from(&instance).unwrap();
+    (instance, witness)
+}
+
+
 #[test]
 fn test_cmz_wallet_with_fee() {
     use group::Group;

src/tests/test_validation_criteria.rs

@@ -103,7 +103,6 @@ mod instance_validation {
         assert!(result.is_err());
     }
 
-
     #[test]
     fn test_empty_string() {
         let rng = &mut rand::thread_rng();