diff --git a/question/format/xml/tests/fixtures/export_category.xml b/question/format/xml/tests/fixtures/export_category.xml
index fcc3474885c..42c9f37e57f 100644
--- a/question/format/xml/tests/fixtures/export_category.xml
+++ b/question/format/xml/tests/fixtures/export_category.xml
@@ -24,6 +24,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber></idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
diff --git a/question/format/xml/tests/fixtures/nested_categories.xml b/question/format/xml/tests/fixtures/nested_categories.xml
index 836e06f07a0..4bf5c2cfca6 100644
--- a/question/format/xml/tests/fixtures/nested_categories.xml
+++ b/question/format/xml/tests/fixtures/nested_categories.xml
@@ -44,6 +44,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber></idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
diff --git a/question/format/xml/tests/fixtures/nested_categories_with_questions.xml b/question/format/xml/tests/fixtures/nested_categories_with_questions.xml
index b4abe7bf4bc..0ea1753f489 100644
--- a/question/format/xml/tests/fixtures/nested_categories_with_questions.xml
+++ b/question/format/xml/tests/fixtures/nested_categories_with_questions.xml
@@ -24,6 +24,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber></idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
@@ -62,6 +63,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>0.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber>K1</idnumber>
     <responseformat>editor</responseformat>
     <responserequired>1</responserequired>
     <responsefieldlines>10</responsefieldlines>
@@ -89,6 +91,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber>K2</idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
@@ -127,6 +130,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber></idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
@@ -165,6 +169,7 @@
     <defaultgrade>1.0000000</defaultgrade>
     <penalty>1.0000000</penalty>
     <hidden>0</hidden>
+    <idnumber></idnumber>
     <answer fraction="100" format="moodle_auto_format">
       <text>true</text>
       <feedback format="html">
diff --git a/question/format/xml/tests/qformat_xml_import_export_test.php b/question/format/xml/tests/qformat_xml_import_export_test.php
index a80c4333300..44d3091241d 100644
--- a/question/format/xml/tests/qformat_xml_import_export_test.php
+++ b/question/format/xml/tests/qformat_xml_import_export_test.php
@@ -366,7 +366,7 @@ class qformat_xml_import_export_test extends advanced_testcase {
                 'attachmentsrequired' => 0,
                 'graderinfo' => ['format' => '1', 'text' => ''],
                 'responsetemplate' => ['format' => '1', 'text' => ''],
-                ]);
+                'idnumber' => 'K1']);
         $kappaquestion1  = $generator->create_question('truefalse', null, [
                 'category' => $categorykappa->id,
                 'name' => 'Kappa Question',
@@ -377,7 +377,8 @@ class qformat_xml_import_export_test extends advanced_testcase {
                 'correctanswer' => '1',
                 'feedbacktrue' => ['format' => '1', 'text' => ''],
                 'feedbackfalse' => ['format' => '1', 'text' => ''],
-                'penalty' => '1']);
+                'penalty' => '1',
+                'idnumber' => 'K2']);
         $categorylambda = $generator->create_question_category([
                 'name' => 'Lambda',
                 'contextid' => '2',