Does either of these tests verify that, if the request _already_ contains a "Signature" param, it isn't added again? I'm trying to see how to easily construct such a test case, but for the moment can't figure out how a user would do that other than e.g. in a brute-force way, e.g.
```
@Test
public void preventDoubleSignature() {
  HttpRequest signedRequest = putBlobWithTime();
  newRequestAuthorizeSignature().replaceAuthorizationHeader(signedRequest, "new-sig");
  assertRequestDoesntContainTwoSigs();
}
```