bug 1502268: marionette: provide informative messages for unexpected alert open error; r=whimboo

Provides specific error messages informing the user what action
was taken with the user prompt, based on the configuration of the
unhandled prompt handler.

Differential Revision: https://phabricator.services.mozilla.com/D10089

--HG--
extra : moz-landing-system : lando

testing/marionette/driver.js

@@ -3229,6 +3229,8 @@ GeckoDriver.prototype._handleUserPrompts = async function() {
     return;
   }
 
+  let {textContent} = this.dialog.ui.infoBody;
+
   let behavior = this.capabilities.get("unhandledPromptBehavior");
   switch (behavior) {
     case UnhandledPromptBehavior.Accept:
@@ -3237,7 +3239,8 @@ GeckoDriver.prototype._handleUserPrompts = async function() {
 
     case UnhandledPromptBehavior.AcceptAndNotify:
       await this.acceptDialog();
-      throw new UnexpectedAlertOpenError();
+      throw new UnexpectedAlertOpenError(
+          `Accepted user prompt dialog: ${textContent}`);
 
     case UnhandledPromptBehavior.Dismiss:
       await this.dismissDialog();
@@ -3245,10 +3248,12 @@ GeckoDriver.prototype._handleUserPrompts = async function() {
 
     case UnhandledPromptBehavior.DismissAndNotify:
       await this.dismissDialog();
-      throw new UnexpectedAlertOpenError();
+      throw new UnexpectedAlertOpenError(
+          `Dismissed user prompt dialog: ${textContent}`);
 
     case UnhandledPromptBehavior.Ignore:
-      throw new UnexpectedAlertOpenError();
+      throw new UnexpectedAlertOpenError(
+          "Encountered unhandled user prompt dialog");
 
     default:
       throw new TypeError(`Unknown unhandledPromptBehavior "${behavior}"`);