Disable ETag checking for Google Cloud Storage

Google Cloud Storage ETag is opaque and not an MD5 hash.

src/test/java/org/gaul/s3proxy/S3AwsSdkTest.java

@@ -28,6 +28,7 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.Random;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 import javax.net.ssl.HostnameVerifier;
@@ -58,6 +59,7 @@ import com.amazonaws.services.s3.model.S3Object;
 import com.amazonaws.services.s3.model.UploadPartRequest;
 import com.amazonaws.services.s3.model.UploadPartResult;
 import com.google.common.base.Throwables;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.io.ByteSource;
 
 import org.assertj.core.api.Fail;
@@ -79,6 +81,11 @@ public final class S3AwsSdkTest {
         disableSslVerification();
     }
 
+    /** Blobstores with opaque ETags. */
+    private static final Set<String> BLOBSTORE_OPAQUE_ETAG = ImmutableSet.of(
+            "azureblob",
+            "google-cloud-storage"
+    );
     private static final ByteSource BYTE_SOURCE = ByteSource.wrap(new byte[1]);
 
     private URI s3Endpoint;
@@ -100,9 +107,8 @@ public final class S3AwsSdkTest {
         info.getBlobStore().createContainerInLocation(null, containerName);
 
         String blobStoreType = context.unwrap().getProviderMetadata().getId();
-        if (blobStoreType.equals("azureblob")) {
-            // AWK SDK checks that ETag matches Content-MD5 during PUT but
-            // Azure returns an opaque ETag.
+        if (BLOBSTORE_OPAQUE_ETAG.contains(blobStoreType)) {
+            // AWK SDK checks that ETag matches Content-MD5 during PUT
             System.setProperty(
                     "com.amazonaws.services.s3.disablePutObjectMD5Validation",
                     "true");