### Question:
S3Link { public URL getUrl() { return getAmazonS3Client().getUrl(getBucketName(), getKey()); } S3Link(S3ClientCache s3cc, String bucketName, String key);   S3Link(S3ClientCache s3cc, Region region, String bucketName, String key); private  S3Link(S3ClientCache s3cc, ID id); String getKey(); String getBucketName(); Region getS3Region(); String toJson(); static S3Link fromJson(S3ClientCache s3cc, String json); AmazonS3Client getAmazonS3Client(); TransferManager getTransferManager(); PutObjectResult uploadFrom(final File source); PutObjectResult uploadFrom(final File source,
            RequestMetricCollector requestMetricCollector); PutObjectResult uploadFrom(final byte[] buffer); PutObjectResult uploadFrom(final byte[] buffer,
            RequestMetricCollector requestMetricCollector); void setAcl(CannedAccessControlList acl); void setAcl(CannedAccessControlList acl, RequestMetricCollector col); void setAcl(AccessControlList acl); void setAcl(AccessControlList acl,
            RequestMetricCollector requestMetricCollector); URL getUrl(); ObjectMetadata downloadTo(final File destination); ObjectMetadata downloadTo(final File destination,
            RequestMetricCollector requestMetricCollector); ObjectMetadata downloadTo(final OutputStream output); ObjectMetadata downloadTo(final OutputStream output,
            RequestMetricCollector requestMetricCollector);  }### Answer:
@Test public void testGetURL() { AWSCredentials credentials = new BasicAWSCredentials("mock", "mock"); StaticCredentialsProvider s3CredentialProvider = new StaticCredentialsProvider(credentials); AmazonS3Client realS3 = new AmazonS3Client(s3CredentialProvider, com.amazonaws.regions.Region.getRegion(Regions.US_WEST_2)); mapper.getS3ClientCache().useClient(realS3); S3Link link = mapper.createS3Link(Region.US_West_2, bucket, key); URL createdURL = realS3.getUrl(bucket, key); URL retrievedURL = link.getUrl(); assertEquals(createdURL, retrievedURL); }