Abstract KMS code with KmsConnection and create a fake KmsConnection

This simplifies the tests for KmsKeyring and KmsUpdater.

This is a followup to []

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148496758

javatests/google/registry/keyring/kms/FakeKmsConnection.java

@@ -0,0 +1,46 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.keyring.kms;
+
+import com.google.common.io.BaseEncoding;
+import java.io.IOException;
+import org.bouncycastle.util.Arrays;
+
+class FakeKmsConnection implements KmsConnection {
+
+  FakeKmsConnection() {}
+
+  /**
+   * Returns a dummy {@link EncryptResponse}.
+   *
+   * <p>The "encrypted value" in the response is the provided value reversed and then base64-encoded
+   * and the name of the cryptoKeyVersion is {@code cryptoKeyName + "/foo"}.
+   */
+  @Override
+  public EncryptResponse encrypt(String cryptoKeyName, byte[] plaintext) throws IOException {
+    return EncryptResponse.create(
+        BaseEncoding.base64().encode(Arrays.reverse(plaintext)), cryptoKeyName + "/foo");
+  }
+
+  /**
+   * Returns a "decrypted" plaintext.
+   *
+   * <p>The plaintext is the encodedCiphertext base64-decoded and then reversed.
+   */
+  @Override
+  public byte[] decrypt(String cryptoKeyName, String encodedCiphertext) throws IOException {
+    return Arrays.reverse(BaseEncoding.base64().decode(encodedCiphertext));
+  }
+}