public Disjunction addOperand(Predicate operand) {
        operands.add(operand);
        return this;
    }
@Test
    void requireThatEqualsIsImplemented() {
        Disjunction lhs = new Disjunction(SimplePredicates.newString("foo"),
                SimplePredicates.newString("bar"));
        assertEquals(lhs, lhs);
        assertNotEquals(lhs, new Object());

        Disjunction rhs = new Disjunction();
        assertNotEquals(lhs, rhs);
        rhs.addOperand(SimplePredicates.newString("foo"));
        assertNotEquals(lhs, rhs);
        rhs.addOperand(SimplePredicates.newString("bar"));
        assertEquals(lhs, rhs);
    }