@Test
    public void testFindSingle() {
        assertEquals(Optional.empty(), Seq.of().findSingle());
        assertEquals(Optional.empty(), Seq.of(1, 2, 3).filter(i -> i > 5).findSingle());
        assertEquals(Optional.of(1), Seq.of(1).findSingle());
        assertThrows(TooManyElementsException.class, () -> Seq.of(1, 2).findSingle());
    }
@author Lukas Eder
@author Roman Tkalenko
jOOL-java-8/src/test/java/org/jooq/lambda/SeqTest.java