@Test
  public void randKeyId_repeatedCallsShouldOutputANegativeValue() {
    assertThat(IntStream.range(0, 100).map(unused -> Util.randKeyId()).min().getAsInt())
        .isAtMost(0);
  }
Tests for Tink internal Util class.
java_src/src/test/java/com/google/crypto/tink/internal/UtilTest.java