Not getting expected missing property/method exception testing Groovy class

Question

While putting together a presentation, I have a situation in which I expect an exception, but I am getting none, when I run my corresponding unit test. What I am doing is incrementally modifying a bean. In this version of the Product and Accessory classes, I have removed the setters/getters for all the properties (save for a setter for one of the Product properties). I have previously converted my classes to use field access notation. So, since I have removed the setters/getters, I am expecting an exception because the field visibility modifiers are private.

Here is the Accessory class:

public class Accessory {
    private String name
    private BigDecimal cost
    private BigDecimal price

    public Accessory() {
        this.cost = BigDecimal.ZERO
        this.price = BigDecimal.ZERO
    }

    public Accessory(String name, BigDecimal cost, BigDecimal price) {
        this.name = name
        this.cost = cost
        this.price = price
    }

    @Override
    public int hashCode() {
        final int prime = 31
        int result = 1
        result = prime * result + ((cost == null) ? 0 : cost.hashCode())
        result = prime * result + ((name == null) ? 0 : name.hashCode())
        result = prime * result + ((price == null) ? 0 : price.hashCode())
        return result
    }

    public boolean equals(Accessory obj) {
        return name == obj.name &&
            cost == obj.cost &&
            price == obj.price
    }

    @Override
    public String toString() {
        return "Accessory [" + "name=" + name + ", cost=" + cost + ", price=" + price + "]"
    }

}

Here are snippets from the Product class:

public class Product {
    private String model
    private List<Accessory> accessories
    private TreeMap<Integer, BigDecimal> priceBreaks
    private BigDecimal cost
    private BigDecimal price
    ...
    public BigDecimal getAccessorizedCost() {
        ...

        for (Accessory pkg : this.accessories) {
            pkgCost = pkgCost.add pkg.cost
        }

        return pkgCost
    }
    ...
}

I would expect that the line pkgCost = pkgCost.add pkg.cost in the above snippet would throw an exception. Likewise, I would think the following asserts in my unit test would do the same:

@Test public void canCreateDefaultInstance() {
    assertNull "Default construction of class ${defaultProduct.class.name} failed to properly initialize model.", defaultProduct.model
    assertTrue "Default construction of class ${defaultProduct.class.name} failed to properly initialize accessories.", defaultProduct.accessories.isEmpty()
    assertTrue "Default construction of class ${defaultProduct.class.name} failed to properly initialize priceBreaks.", defaultProduct.priceBreaks.isEmpty()
    assertEquals "Default construction of class ${defaultProduct.class.name} failed to properly initialize cost.", BigDecimal.ZERO, defaultProduct.cost as BigDecimal
    assertEquals "Default construction of class ${defaultProduct.class.name} failed to properly initialize price.", BigDecimal.ZERO, defaultProduct.price as BigDecimal
}

Here are the metaclass properties and methods:

MetaClass Properties are:
[accessorizedCost, accessorizedPrice, class, priceBreaks]
MetaClass Methods are:
[__$swapInit, addPriceBreak, calcDiscountMultiplierFor, calcVolumePriceFor, equals, getAccessorizedCost, getAccessorizedPrice, getClass, getMetaClass, getProperty, hashCode, invokeMethod, notify, notifyAll, setMetaClass, setPriceBreaks, setProperty, toString, wait]

You can see, for example, that there are no properties nor corresponding getter/setters for the privately defined model, accessories, cost and price fields. So, like the line in the Product class not failing when referencing the cost property of Accessory, I do not understand how the unit tests can pass when there is not property nor getter/setters for these private fields.

I am compiling using Groovy 2.0.4 and running Eclipse.

What am I missing or not understanding?