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