test: Add more tests for light_utils main module

Achieve full coverage there.

utils/src/lib.rs

@@ -48,12 +48,12 @@ impl From<UtilsError> for solana_program::program_error::ProgramError {
     }
 }
 
-pub fn is_smaller_than_bn254_field_size_be(bytes: &[u8; 32]) -> Result<bool, UtilsError> {
+pub fn is_smaller_than_bn254_field_size_be(bytes: &[u8; 32]) -> bool {
     let bigint = BigUint::from_bytes_be(bytes);
     if bigint < ark_bn254::Fr::MODULUS.into() {
-        Ok(true)
+        true
     } else {
-        Ok(false)
+        false
     }
 }
 
@@ -67,7 +67,7 @@ pub fn hash_to_bn254_field_size_be(bytes: &[u8]) -> Option<([u8; 32], u8)> {
             // Truncates to 31 bytes so that value is less than bn254 Fr modulo
             // field size.
             hashed_value[0] = 0;
-            if let Ok(true) = is_smaller_than_bn254_field_size_be(&hashed_value) {
+            if is_smaller_than_bn254_field_size_be(&hashed_value) {
                 return Some((hashed_value, bump_seed[0]));
             }
         }
@@ -109,11 +109,28 @@ pub fn rustfmt(code: String) -> Result<Vec<u8>, anyhow::Error> {
 
 #[cfg(test)]
 mod tests {
-
+    use num_bigint::ToBigUint;
     use solana_program::pubkey::Pubkey;
 
+    use crate::bigint::bigint_to_be_bytes_array;
+
     use super::*;
 
+    #[test]
+    fn test_is_smaller_than_bn254_field_size_be() {
+        let modulus: BigUint = ark_bn254::Fr::MODULUS.into();
+        let modulus_bytes: [u8; 32] = bigint_to_be_bytes_array(&modulus).unwrap();
+        assert!(!is_smaller_than_bn254_field_size_be(&modulus_bytes));
+
+        let bigint = modulus.clone() - 1.to_biguint().unwrap();
+        let bigint_bytes: [u8; 32] = bigint_to_be_bytes_array(&bigint).unwrap();
+        assert!(is_smaller_than_bn254_field_size_be(&bigint_bytes));
+
+        let bigint = modulus + 1.to_biguint().unwrap();
+        let bigint_bytes: [u8; 32] = bigint_to_be_bytes_array(&bigint).unwrap();
+        assert!(!is_smaller_than_bn254_field_size_be(&bigint_bytes));
+    }
+
     #[test]
     fn test_hash_to_bn254_field_size_be() {
         for _ in 0..10_000 {
@@ -122,7 +139,7 @@ mod tests {
                 .expect("Failed to find a hash within BN254 field size");
             assert_eq!(bump, 255, "Bump seed should be 0");
             assert!(
-                is_smaller_than_bn254_field_size_be(&hashed_value).unwrap(),
+                is_smaller_than_bn254_field_size_be(&hashed_value),
                 "Hashed value should be within BN254 field size"
             );
         }