@Test
    void allMatch() {
        assertTrue(instance.allMatch(ELEMENT::equals));
        assertFalse(SingletonStream.of(OTHER_ELEMENT).allMatch(ELEMENT::equals));

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