Add explicit test for empty string in test_validation_criteria

Author: mmaker

src/linear_relation/mod.rs

@@ -681,12 +681,6 @@ impl<G: PrimeGroup> TryFrom<&LinearRelation<G>> for CanonicalLinearRelation<G> {
             ));
         }
 
-        // if relation.linear_map.linear_combinations.is_empty() {
-        //     return Err(InvalidInstance::new(
-        //         "Empty relations cannot be proven"
-        //     ));
-        // }
-
         // If any linear combination is empty, the relation is invalid
         if relation
             .linear_map

src/tests/test_validation_criteria.rs

@@ -5,7 +5,7 @@
 
 #[cfg(test)]
 mod instance_validation {
-    use crate::{linear_relation::{CanonicalLinearRelation, LinearRelation}, tests::spec::rng};
+    use crate::linear_relation::{CanonicalLinearRelation, LinearRelation};
     use bls12_381::{G1Projective as G, Scalar};
 
     #[test]
@@ -131,6 +131,16 @@ mod instance_validation {
         assert!(result.is_err());
     }
 
+
+    #[test]
+    fn test_empty_string() {
+        let rng = &mut rand::thread_rng();
+        let relation = LinearRelation::<G>::new();
+        let nizk = relation.into_nizk(b"test_session").unwrap();
+        let narg_string = nizk.prove_batchable(&vec![], rng).unwrap();
+        assert!(narg_string.is_empty());
+    }
+
     #[test]
     fn without_witness() {
         let B = G::generator();