public function signMustKeepAFluentInterface() : Builder
{
$signer = $this->createMock(Signer::class);
$signature = $this->createMock(Signature::class);
$signer->expects($this->any())->method('sign')->willReturn($signature);
$builder = $this->createBuilder();
self::assertSame($builder, $builder->sign($signer, new Key('test')));
return $builder;
}