Bug 1685090 - [devtools] Print exceptions when importing functions thrown in browser toolbox tests. r=jdescottes

Without this, we were silently ignoring many errors when evaluating a piece of JS.
Imported function may still work, but were missing global variables. Very misleading!

Differential Revision: https://phabricator.services.mozilla.com/D100927

devtools/client/framework/browser-toolbox/test/helpers-browser-toolbox.js

@@ -155,7 +155,14 @@ async function initBrowserToolboxTask({
   }
 
   async function importScript(script) {
-    await consoleFront.evaluateJSAsync(script);
+    const response = await consoleFront.evaluateJSAsync(script);
+    if (response.hasException) {
+      ok(
+        false,
+        "ToolboxTask.spawn exception while importing script: " +
+          response.exceptionMessage
+      );
+    }
   }
 
   async function destroy() {