2 Why We Need Model-Based Testing

168 Modeling Systems with Structured State
}
[Action]
static void DeleteObject(string obj)
{
references = references.Remove(obj);
}
If you were to explore this model program you would notice that the following
two traces result in the same end state:
Trace 1 Trace 2
AddReference("objA") AddReference("objA")
RemoveReference("objA") AddReference("objA")
AddReference("objA") RemoveReference("objA")
RemoveReference("objA") RemoveReference("objA")
DeleteObject("objA") DeleteObject("objA")
Creating bags
The easiest way to create a new bag is to list the elements in the constructor. The
order in which arguments appear doesn’t matter, and duplicates will be used as many
times as they appear:
Bag cities = new Bag("Athens", "Rome", "Athens",
"Paris", "New York", "Seattle");
Assert.AreEqual(cities.Count, 6);
You can also create a bag from an IEnumerable object:
static Bag ConvertToBag(IEnumerable list)
{
return new Bag(list);
}
Like sets, bags implement the IEnumerable interface, so they can be used iteratively.
If an element appears in a bag more than once, iteration will include it more
than once. If you want to get access to the unique values found in a bag, you can
use the Keys property.
Iteration over bags occurs in an arbitrary order.
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