add error test case

compiler/can/src/builtins.rs

@@ -2326,7 +2326,7 @@ fn list_replace(symbol: Symbol, var_store: &mut VarStore) -> Def {
     // Otherwise, return the list unmodified.
     let body = If {
         cond_var: bool_var,
-        branch_var: var_store.fresh(),
+        branch_var: ret_result_var,
         branches: vec![(
             // if-condition
             no_region(

compiler/test_gen/src/gen_list.rs

@@ -1780,6 +1780,23 @@ fn replace_unique_int_list() {
     );
 }
 
+#[test]
+#[cfg(any(feature = "gen-llvm"))]
+fn replace_unique_int_list_out_of_bounds() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+                result = List.replace [ 12, 9, 7, 1, 5 ] 5 33
+                when result is
+                    Ok {value} -> value
+                    Err OutOfBounds -> -1 
+            "#
+        ),
+        -1,
+        i64
+    );
+}
+
 #[test]
 #[cfg(any(feature = "gen-llvm"))]
 fn replace_unique_int_list_get_old_value() {