reverted:
--- b/core/modules/system/src/Tests/File/NameMungingTest.php
+++ a/core/modules/system/src/Tests/File/NameMungingTest.php
@@ -66,14 +66,10 @@
    * White listed extensions are ignored by file_munge_filename().
    */
   function testMungeIgnoreWhitelisted() {
+    // Declare our extension as whitelisted. The declared extensions should
+    // be case insensitive so test using one with a different case.
-    // Declare our extension as whitelisted.
-    // The declared extensions should be case insensitive.
-    // Test using one with a different case.
     $munged_name = file_munge_filename($this->nameWithUcExt, $this->badExtension);
     $this->assertIdentical($munged_name, $this->nameWithUcExt, format_string('The new filename (%munged) matches the original (%original) once the extension has been whitelisted.', array('%munged' => $munged_name, '%original' => $this->nameWithUcExt)));
-    // Test with same case.
-    $munged_name = file_munge_filename($this->name, $this->badExtension);
-    $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) when case of the extension is the same as that whitelisted.', array('%munged' => $munged_name, '%original' => $this->name)));
     // The allowed extensions should also be normalized.
     $munged_name = file_munge_filename($this->name, strtoupper($this->badExtension));
     $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) also when the whitelisted extension is in uppercase.', array('%munged' => $munged_name, '%original' => $this->name)));
only in patch2:
unchanged:
--- a/core/tests/Drupal/KernelTests/Core/File/NameMungingTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/NameMungingTest.php
@@ -70,6 +70,9 @@ function testMungeIgnoreWhitelisted() {
     // be case insensitive so test using one with a different case.
     $munged_name = file_munge_filename($this->nameWithUcExt, $this->badExtension);
     $this->assertIdentical($munged_name, $this->nameWithUcExt, format_string('The new filename (%munged) matches the original (%original) once the extension has been whitelisted.', array('%munged' => $munged_name, '%original' => $this->nameWithUcExt)));
+    // Test with same case.
+    $munged_name = file_munge_filename($this->name, $this->badExtension);
+    $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) when case of the extension is the same as that whitelisted.', array('%munged' => $munged_name, '%original' => $this->name)));
     // The allowed extensions should also be normalized.
     $munged_name = file_munge_filename($this->name, strtoupper($this->badExtension));
     $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) also when the whitelisted extension is in uppercase.', array('%munged' => $munged_name, '%original' => $this->name)));