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    @Test
    public void testSwitchIfEmptyProperlyClosesReplacementStream() {
        final boolean[] closed = new boolean[] { false };
        final Stream<Integer> replacementStream = Stream.of(1, 2, 3)
                .onClose(() -> {
                    closed[0] = true;
                });
        final Stream<Integer> integerStream = StreamUtils.switchIfEmpty(Stream.empty(), () -> replacementStream);
        assertEquals(Arrays.asList(1, 2, 3), integerStream.collect(Collectors.toList()));
        integerStream.close();
        assertTrue(closed[0]);
    }

    @Test
    public void doesNotThrowExceptionUntilNextCall_whenHasNextReturnsTrueButNextThrows() {
        // this test validates that if attempting to retrieve an item throws
        // an exception, that exception is not thrown until the appropriate
        // next/peek call happens.
        // in this instance, the delegate is actually returning "true" when
        // asked if it has next, and then calling next throws an exception.
        // we want to preserve that behavior
        when(mockIterator.hasNext()).thenReturn(true);
        when(mockIterator.next()).thenThrow(new RuntimeException());

        assertTrue(peekingIterator.hasNext());
        boolean caught = false;
        try {
            peekingIterator.peek();
        } catch(Exception e) {
            caught = true;
        }
        assertTrue(caught);
        caught = false;
        try {
            peekingIterator.next();
        } catch(Exception e) {
            caught = true;
        }
        assertTrue(caught);
    }