MDL-74302 mod_quiz: Users with preview cap should see prevent messages

mod/quiz/tests/behat/preview.feature

@@ -69,6 +69,7 @@ Feature: Preview a quiz as a teacher
       | TF1      | 1    |         |
       | TF2      | 1    | 3.0     |
     When I am on the "Quiz 2" "mod_quiz > View" page logged in as "admin"
+    And I should see "This quiz is not currently available"
     And I press "Preview quiz"
     Then I should see "if this were a real attempt, you would be blocked" in the ".alert-warning" "css_element"
 

mod/quiz/view.php

@@ -229,14 +229,18 @@ if (!$viewobj->quizhasquestions) {
         }
     }
 
-    // If this is not a preview and, so far, we think a button should be printed, so check if they will be
-    // allowed to access it.
-    if (!$canpreview && $viewobj->buttontext) {
+    // Users who can preview the quiz should be able to see all messages for not being able to access the quiz.
+    if ($canpreview) {
+        $viewobj->preventmessages = $viewobj->accessmanager->prevent_access();
+    } else if ($viewobj->buttontext) {
+        // If, so far, we think a button should be printed, so check if they will be allowed to access it.
         if (!$viewobj->moreattempts) {
             $viewobj->buttontext = '';
-        } else if ($canattempt
-                && $viewobj->preventmessages = $viewobj->accessmanager->prevent_access()) {
-            $viewobj->buttontext = '';
+        } else if ($canattempt) {
+            $viewobj->preventmessages = $viewobj->accessmanager->prevent_access();
+            if ($viewobj->preventmessages) {
+                $viewobj->buttontext = '';
+            }
         }
     }
 }