### Question:
CompoundCertificatePool extends CertificatePool { @Override public CertificateToken getIssuer(final Token token) { List<CertificateToken> issuers = getIssuers(token); if (Utils.isCollectionNotEmpty(issuers)) { for (CertificateToken issuer : issuers) { if (issuer.isValidOn(token.getCreationDate())) { return issuer; } } logger.warn("No issuer found for the token creation date. The process continues with an issuer which has the same public key."); return issuers.iterator().next(); } else { return null; } } 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 getIssuerShouldReturnNothingIfNotPresentInEitherPool() { Assert.assertEquals(null, compoundCertificatePool.getIssuer(testCertificateToken)); }