@Test
    void forEachOrdered() {
        final List<String> strings = new ArrayList<>();
        instance.forEachOrdered(strings::add);
        assertEquals(1, strings.size());

        assertThrows(IllegalStateException.class, () -> instance.forEachOrdered(strings::add));
    }
Test of mapToInt method, of class SingletonStream.
common-parent/singletonstream/src/test/java/com/speedment/common/singletonstream/SingletonStreamTest.java