### Question:
Signer { public Authorization sign(RequestContent requestContent) { return sign(requestContent, requestContent.getHeaderNames()); } Signer(Keychain keychain);  Signer(Key singleKey, KeyId keyId);  Signer(Keychain keychain, KeyId keyId); Keychain getKeychain(); Keychain getCandidateKeys(); KeyId getKeyId(); synchronized boolean rotateKeys(); synchronized boolean rotateKeys(Challenge nextChallenge); synchronized boolean rotateKeys(Challenge nextChallenge, Authorization failedAuthz); Authorization sign(RequestContent requestContent); Authorization sign(RequestContent requestContent, List<String> electiveHeaders);  }### Answer:
@Test public void testSign() { }