Test Template Framework

The Test Template Framework (TTF) is a model-based testing (MBT) framework proposed by Phil Stocks and David Carrington in (Stocks & Carrington 1996) for the purpose of software testing. Although the TTF was meant to be notation-independent, the original presentation was made using the Z formal notation. It is one of the few MBT frameworks approaching unit testing.

Introduction

The TTF is a specific proposal of model-based testing (MBT). It considers models to be Z specifications. Each operation within the specification is analyzed to derive or generate abstract test cases. This analysis consists of the following steps:

  1. Define the input space (IS) of each operation.
  2. Derive the valid input space (VIS) from the IS of each operation.
  3. Apply one or more testing tactics,[1] starting from each VIS, to build a testing tree for each operation. Testing trees are populated with nodes called test classes.
  4. Prune each of the resulting testing trees.
  5. Find one or more abstract test cases from each leaf in each testing tree.

One of the main advantages of the TTF is that all of these concepts are expressed in the same notation of the specification, i.e. the Z notation. Hence, the engineer has to know only one notation to perform the analysis down to the generation of abstract test cases.

Important concepts

In this section the main concepts defined by the TTF are described.

Input space

Let be a Z operation. Let be all the input and (non-primed) state variables referenced in , and their corresponding types. The Input Space (IS) of , written , is the Z schema box defined by .

Valid input space

Let be a Z operation. Let be the precondition of . The Valid Input Space (VIS) of , written , is the Z schema box defined by .

Test class

Let be a Z operation and let be any predicate depending on one or more of the variables defined in . Then, the Z schema box is a test class of . Note that this schema is equivalent to . This observation can be generalized by saying that if is a test class of , then the Z schema box defined by is also a test class of . According to this definition the VIS is also a test class.

If is a test class of , then the predicate in is said to be the characteristic predicate of or is characterized by .

Test classes are also called test objectives (Utting & Legeard 2007), test templates (Stocks & Carrington 1996) and test specifications.

Testing tactic

In the context of the TTF a testing tactic[1] is a means to partition any test class of any operation. However, some of the testing tactics used in practice actually do not always generate a partition of some test classes.

Some testing tactics originally proposed for the TTF are the following:

Some other testing tactics that may also be used are the following:

Testing tree&

The application of a testing tactic to the VIS generates some test classes. If some of these test classes are further partitioned by applying one or more testing tactics, a new set of test classes is obtained. This process can continue by applying testing tactics to the test classes generated so far. Evidently, the result of this process can be drawn as a tree with the VIS as the root node, the test classes generated by the first testing tactic as its children, and so on. Furthermore, Stocks and Carrington in (Stocks & Carrington 1996) propose to use the Z notation to build the tree, as follows.

Pruning testing trees

In general a test class' predicate is a conjunction of two or more predicates. It is likely, then, that some test classes are empty because their predicates are contradictions. These test classes must be pruned from the testing tree because they represent impossible combinations of input values, i.e. no abstract test case can be derived out of them.

Abstract test case

An abstract test case is an element belonging to a test class. The TTF prescribes that abstract test cases should be derived only from the leaves of the testing tree. Abstract test cases can also be written as Z schema boxes. Let be some operation, let be the VIS of , let be all the variables declared in , let be a (leaf) test class of the testing tree associated to , let be the characteristic predicates of each test class from up to (by following the edges from child to parent), and let be constant values satisfying . Then, an abstract test case of is the Z schema box defined by .

See also

References

Notes

  1. 1 2 Stocks and Carrington use the term testing strategies in (Stocks & Carrington 1996).
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