public function testShouldValidateKeysWhenThereAreMissingNonRequiredKeys()
{
$input = ['foo' => 42];
$key1 = new Key('foo', new AlwaysValid(), true);
$key2 = new Key('bar', new AlwaysValid(), false);
$keySet = new KeySet($key1, $key2);
$this->assertTrue($keySet->validate($input));
}