[Metadata] Throw rewriting error when testing

Change-Id: Icf5515af1d111ea4936e595e661902bbabd31848
diff --git a/src/main/java/com/android/tools/r8/kotlin/KotlinMetadataRewriter.java b/src/main/java/com/android/tools/r8/kotlin/KotlinMetadataRewriter.java
index 0ff0070..fb6575c 100644
--- a/src/main/java/com/android/tools/r8/kotlin/KotlinMetadataRewriter.java
+++ b/src/main/java/com/android/tools/r8/kotlin/KotlinMetadataRewriter.java
@@ -182,6 +182,13 @@
               writeMetadataFieldInfo);
       clazz.setAnnotations(clazz.annotations().rewrite(anno -> anno == oldMeta ? newMeta : anno));
     } catch (Throwable t) {
+      assert appView.checkForTesting(
+          () -> {
+            throw appView
+                .options()
+                .reporter
+                .fatalError(KotlinMetadataDiagnostic.unexpectedErrorWhenRewriting(clazz.type, t));
+          });
       appView
           .options()
           .reporter