try {
      unmod.computeIfAbsent(3, (k) -> k + "three");
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.computeIfPresent(4, (k, v) -> v);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.compute(4, (k, v) -> v);