fix: Format non-error exceptions (#14604)

This commit adds "Deno.core.setFormatExceptionCallback" which
can be used to provide custom formatting for errors. It is useful
in cases when user throws something that is non-Error (eg.
a string, plain object, etc).

1 files changed, 4 insertions, 2 deletions

diff --git a/runtime/js/40_testing.js b/runtime/js/40_testing.js
index 8c7d69fb0..865482042 100644
--- a/runtime/js/40_testing.js
+++ b/runtime/js/40_testing.js
@@ -217,14 +217,16 @@
 
       let msg = `Test case is leaking async ops.
 
-- ${ArrayPrototypeJoin(details, "\n - ")}`;
+ - ${ArrayPrototypeJoin(details, "\n - ")}`;
 
       if (!core.isOpCallTracingEnabled()) {
         msg +=
           `\n\nTo get more details where ops were leaked, run again with --trace-ops flag.`;
+      } else {
+        msg += "\n";
       }
 
-      throw msg;
+      throw assert(false, msg);
     };
   }