private ColumnId(String id) {
        this.id = id;
    }
@Test
    public void testColumnId() {
        ColumnId columnIdA = ColumnId.create("a");

        Assert.assertTrue(columnIdA.equals(columnIdA));
        Assert.assertTrue(columnIdA.equals(ColumnId.create("a")));
        Assert.assertFalse(columnIdA.equals(ColumnId.create("A")));
        Assert.assertFalse(columnIdA.equals(ColumnId.create("b")));

        Assert.assertTrue(columnIdA.equalsIgnoreCase(columnIdA));
        Assert.assertTrue(columnIdA.equalsIgnoreCase(ColumnId.create("a")));
        Assert.assertTrue(columnIdA.equalsIgnoreCase(ColumnId.create("A")));
        Assert.assertFalse(columnIdA.equalsIgnoreCase(ColumnId.create("b")));
    }