Basic Terms

• Explicit parameter - An object that is explicitly declared in the method signature, see Figure 1.

• Implict parameter - An object that is visible to the method by virtue of the fact that it is declared as a class or instance variable in the class declaration. Not all of the data attributes in the class are visible to all the methods in the class. Syntactically all the protected and the public attributes are visible to a derived class during inheritance. Therefore the implicit parameters for a derived class includes the attributes of the base class that are visible to the derived class. A detailed set of counting rules for parameters are presented in section 3.7.

• Constant Object - A constant object is one that does not change its state during the execution of the method. These consist of objects that are made state invariant syntactically by definition, such as const objects in C++ or final objects in Java.

• Constant method - A constant method is one that does not modify any objects. This includes implicit and explicit parameters.

An explicit parameter can be either a modifiable or an inspectable object with respect to a specific method. The classification is determined by whether the object changes its state during the execution of the method. For the implementation of the metric being presented in this paper, all the implicit parameters are assumed to be modifiable objects. This metric is applied to the specification of a class which will not provide sufficient information to determine which of the implicit parameters might be modified. This assumption will make our metric value an upper bound on the effort estimation.

The attributes that are available for calculating the testability metric are the attributes defined in the class, the parameters declared in the method signatures and the attributes that are visible to the methods due to inheritance and aggregation.