White listed extensions are ignored by file_munge_filename().
function testMungeIgnoreWhitelisted() {
// Declare our extension as whitelisted.
$munged_name = file_munge_filename($this->name, $this->bad_extension);
$this
->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) once the extension has been whitelisted.', array(
'%munged' => $munged_name,
'%original' => $this->name,
)));
}