diff -u b/core/modules/system/src/Tests/File/NameMungingTest.php b/core/modules/system/src/Tests/File/NameMungingTest.php
--- b/core/modules/system/src/Tests/File/NameMungingTest.php
+++ b/core/modules/system/src/Tests/File/NameMungingTest.php
@@ -71,13 +71,14 @@
    * White listed extensions are ignored by file_munge_filename().
    */
   function testMungeIgnoreWhitelisted() {
-    // Most commonly,  extensions are same casing and we expect no changes.
-    $munged_name = file_munge_filename($this->name, $this->badExtension);
-    $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) when casing of the extension is same as the whitelisted.', array('%munged' => $munged_name, '%original' => $this->name)));
-    // 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)));
@@ -93,2 +94,3 @@
   }
+
 }