@Test
  public void testKeyManagerRegistered() throws Exception {
    assertThat(
            KeyManagerRegistry.globalInstance()
                .getUntypedKeyManager("type.googleapis.com/google.crypto.tink.PrfBasedDeriverKey"))
        .isNotNull();
  }
We test newKeyData directly because PrfBasedDeriverKeyManager has its own implementation.
java_src/src/test/java/com/google/crypto/tink/keyderivation/internal/PrfBasedDeriverKeyManagerTest.java