@Test
void testPutAllMultiMapSimple() {

    MultiMap<String> mm = new MultiMap<>();
    assertMapSize(mm, 0); // Shouldn't have anything yet.
    MultiMap<String> input = new MultiMap<>();
    input.put("food", "apple");
    input.put("color", "red");
    input.put("amount", "bushel");
    mm.putAll(input);
    assertMapSize(mm, 3);
    assertValues(mm, "food", "apple");
    assertValues(mm, "color", "red");
    assertValues(mm, "amount", "bushel");
}