private static String removePrefix(String expectedPrefix, String kmsKeyUri) {
    if (!kmsKeyUri.toLowerCase(Locale.US).startsWith(expectedPrefix)) {
      throw new IllegalArgumentException(
          String.format("key URI must start with %s", expectedPrefix));
    }
    return kmsKeyUri.substring(expectedPrefix.length());
  }
@return true either if this client is a generic one and uri starts with {@link
    FakeKmsClient#PREFIX}, or the client is a specific one that is bound to the key identified
    by {@code uri}.
java_src/src/main/java/com/google/crypto/tink/testing/FakeKmsClient.java