Here are the ones I wrote if they help:

const sqr = once((x) => { return x * x})
Test.assertEquals(sqr(3), 9)
Test.assertEquals(sqr(5), undefined)

const add = once((a,b) => { return a + b })
Test.assertEquals(add(1,2), 3)
Test.assertEquals(add(5,9), undefined)
Test.assertNotEquals(add(1,2), 3)