Try to load a non-existent file by URI.
function testLoadMissingFilepath() {
$files = file_load_multiple(array(), array(
'uri' => 'foobar://misc/druplicon.png',
));
$this
->assertFalse(reset($files), "Try to load a file that doesn't exist in the database fails.");
$this
->assertFileHooksCalled(array());
}