FIX Remove any extra added tabs from SingleTabPage

code/multitab-validation/SingleTabPage.php

@@ -4,6 +4,7 @@ namespace SilverStripe\FrameworkTest\Model;
 
 use Page;
 use SilverStripe\Forms\RequiredFields;
+use SilverStripe\Forms\Tab;
 
 if (!class_exists(Page::class)) {
     return;
@@ -22,4 +23,22 @@ class SingleTabPage extends Page
             'Content'
         ]);
     }
+
+    public function getCMSFields()
+    {
+        $fields = parent::getCMSFields();
+        // Page may will extend CWP BasePage if running in a kitchen-sink context,
+        // so removing any extra tabs added - this class is for a "single tab" test
+        $tabFieldNames = [];
+        foreach ($fields->flattenFields() as $field) {
+            $fieldName = $field->getName();
+            if (is_a($field, Tab::class) && $fieldName !== 'Main') {
+                $tabFieldNames[] = $fieldName;
+            }
+        }
+        foreach ($tabFieldNames as $tabFieldName) {
+            $fields->removeByName($tabFieldName);
+        }
+        return $fields;
+    }
 }