add test for right bit shift with assignment (#703)

* add test for bit shift right with assignment

* fixed comment

Co-authored-by: Martina <martina@martina>

felt/src/lib.rs

@@ -189,5 +189,17 @@ mod test {
             prop_assert!(as_uint < p, "{}", as_uint);
             prop_assert_eq!(&(q * y), x);
         }
+
+        #[test]
+         // Property-based test that ensures, for 100 {value}s that are randomly generated each time tests are run, that performing a bit shift to the right by {shift_amount} of bits (between 0 and 999), with assignment, returns a result that is inside of the range [0, p].
+         // "With assignment" means that the result of the operation is autommatically assigned to the variable value, replacing its previous content.
+         fn shift_right_assign_in_range(ref value in "(0|[1-9][0-9]*)", ref shift_amount in "[0-9]{1,3}"){
+            let mut value = Felt::parse_bytes(value.as_bytes(), 10).unwrap();
+            let p = FeltBigInt::parse_bytes(PRIME_STR[2..].as_bytes(), 16).unwrap();
+            let shift_amount:usize = shift_amount.parse::<usize>().unwrap();
+            value >>= shift_amount;
+            value.to_biguint();
+            prop_assert!(value < p);
+        }
     }
 }