* impossible. We want the test, though, in case that changes in the future,
     * so we use isInstance instead.
     */
    assertFalse(
        "Can't test the main listenInPoolThread path "
            + "if the input is already a ListenableFuture",
        ListenableFuture.class.isInstance(input));
    ListenableFuture<String> listenable = listenInPoolThread(input);
    /*

     * impossible. We want the test, though, in case that changes in the future,
     * so we use isInstance instead.
     */
    assertFalse(
        "Can't test the main listenInPoolThread path "
            + "if the input is already a ListenableFuture",
        ListenableFuture.class.isInstance(input));
    ListenableFuture<String> listenable = listenInPoolThread(input);
    /*