diff --git a/tests/testutils/src/lib.rs b/tests/testutils/src/lib.rs
index d181e455b1..abd28f26d2 100644
--- a/tests/testutils/src/lib.rs
+++ b/tests/testutils/src/lib.rs
@@ -22,8 +22,8 @@ fn read_text(path: &Path) -> String {
 }
 
 pub fn dir_tests<F>(paths: &[&str], f: F)
-where
-    F: Fn(&str) -> String,
+    where
+        F: Fn(&str) -> String,
 {
     for path in collect_tests(paths) {
         let actual = {
@@ -73,16 +73,24 @@ fn test_from_dir(dir: &Path) -> Vec<PathBuf> {
     acc
 }
 
+const REWRITE: bool = false;
+
 fn print_difference(expected: &str, actual: &str, path: &Path) {
     let dir = project_dir();
     let path = path.strip_prefix(&dir).unwrap_or_else(|_| path);
     if expected.trim() == actual.trim() {
         println!("whitespace difference, rewriting");
+        println!("file: {}\n", path.display());
         file::put_text(path, actual).unwrap();
-    } else {
-        let changeset = Changeset::new(actual, expected, "\n");
-        print!("{}", changeset);
+        return;
     }
+    if REWRITE {
+        println!("rewriting {}", path.display());
+        file::put_text(path, actual).unwrap();
+        return;
+    }
+    let changeset = Changeset::new(actual, expected, "\n");
+    print!("{}", changeset);
     println!("file: {}\n", path.display());
     panic!("Comparison failed")
 }