### Question:
CompoundCertificatePool extends CertificatePool { @Override public Set<CertificateSourceType> getSources(CertificateToken certificateToken) { return mergeToSet(getTrustedCertificatePool().getSources(certificateToken), super.getSources(certificateToken)); } CompoundCertificatePool(CertificateSource trustedCertificateSource); @Override CertificateToken getInstance(final CertificateToken certificateToAdd, final CertificateSourceType certSource); @Override boolean isTrusted(CertificateToken cert); @Override Set<CertificateSourceType> getSources(CertificateToken certificateToken); @Override List<CertificateToken> getIssuers(final Token token); @Override CertificateToken getIssuer(final Token token); @Override CertificateToken getTrustAnchor(CertificateToken cert); @Override Set<CertificateToken> get(X500Principal x500Principal); @Override List<CertificateToken> get(PublicKey publicKey); @Override List<CertificateToken> getBySki(final byte[] expectedSki); @Override List<CertificateToken> getBySignerId(SignerId signerId); @Override void importCerts(final CertificateSource certificateSource); @Override int getNumberOfEntities(); @Override int getNumberOfCertificates(); @Override List<CertificateToken> getCertificateTokens();  }### Answer:
@Test public void getSourcesShouldReturnNothingIfCertificateNotPresentAnywhere() { Assert.assertEquals(Collections.emptySet(), trustedCertificatePool.getSources(testCertificateToken)); Assert.assertEquals(Collections.emptySet(), compoundCertificatePool.getSources(testCertificateToken)); }