public function unlinkCanNotRemoveNonEmptyDirectory()
{
try {
$this->assertFalse(unlink($this->barURL));
} catch (\PHPUnit_Framework_Error $fe) {
$this->assertEquals('unlink(vfs://foo/bar): Operation not permitted', $fe->getMessage());
}
$this->assertTrue($this->foo->hasChild('bar'));
$this->assertFileExists($this->barURL);
}