diff --git a/core/modules/block/tests/src/Unit/Plugin/DisplayVariant/FullPageVariantTest.php b/core/modules/block/tests/src/Unit/Plugin/DisplayVariant/FullPageVariantTest.php
index 1cbcfe5..6d8b785 100644
--- a/core/modules/block/tests/src/Unit/Plugin/DisplayVariant/FullPageVariantTest.php
+++ b/core/modules/block/tests/src/Unit/Plugin/DisplayVariant/FullPageVariantTest.php
@@ -135,6 +135,11 @@ public function testBuild() {
         'block3' => array(),
         '#sorted' => TRUE,
       ),
+      // Content region is always added by
+      // \Drupal\block\Plugin\DisplayVariant\FullPageVariant
+      'content' => array(
+        'system_main' => NULL,
+      ),
     );
     $this->assertSame($expected, $display_variant->build());
   }