Basis Path Testing - A white Box testing technique.

Basis Path Testing uses the algorithmic flow of the program to design tests. Test cases that are written to test the basis set execute every statement in the program at least once.

- A flow graph should be drawn only when the logical structure of a component is complex. The flow graph allows you to trace program paths more readily. When compound conditions are encountered in a procedural design, the generation of a flow graph becomes slightly more complicated.

- Independent program path is a path which has at least one new set of processing statements or a new condition. An independent path should move along one edge that has not been traversed before. To know how many paths to look for, cyclomatic complexity is a useful metric for predicting those modules that are likely to be error prone. It can be used for test planning as well as test case design. Cyclomatic complexity provides the upper bound on the number of test cases that will be required to guarantee that every statement in the program has been executed at least one time.

- There are few steps to derive test cases or the basis set.
A flow graph is drawn using the design or code.
The cyclomatic complexity of flow graph is evaluated.
A basis set of linear independent path is determined.
Test cases are prepared forcing the execution of each path in basis set.

- Graph matrix is a square matrix whose size is equal to the number of nodes on flow graph. It is a tabular representation of a flow graph. Adding link weight to the each matrix entry, graph matrix can become a powerful tool to evaluate program control structure during testing.

Flow oriented Modeling - Creating a Control Flow Diagram and The Control Specification

Flow models focus on the flow of data objects as they are transformed by processing functions. There are applications which are driven by events rather than data and produce information that is controlled and process information keeping in mind the time and performance. In such situations, control flow diagrams comes into picture along with data flow modeling.

There are some guidelines to select potential events for a control flow diagram:
- all sensors that are read by the software are listed.
- all interrupt conditions are listed.
- all switches actuated by operator are listed.
- all data conditions are listed.
- all control items are reviewed.
- all states that describe the behavior of a system are listed.
- all transitions between states are defined.
- all possible omissions should be kept in focus.

The Control Specification contains a state diagram which is sequential specification of behavior. It contains a program activation table which is a combinatorial specification of behavior. Control specification does not give any information about the inner working of the processes activated as a result of this behavior.

What is Cyclomatic Complexity and how it is computed?

Cyclomatic complexity measures the amount of decision logic in a single software module. It provides a quantitative measure of the logical complexity of a program. It gives the number of recommended test for software. When used in the context of basis path testing method, the value computed for Cyclomatic complexity defines the number for independent paths in the basis set of a program and provides us an upper bound for the number of tests that must be conducted to ensure that all statements have been executed at least once.
An independent path is any path through the program that introduces at least one new set of processing statements or a new condition.

Control flow graphs describe the logic structure of software module. Each flow consists of nodes and edges. Nodes are computation statements or expresions.
Edges represent transfer of control between nodes.Each possible execution path of a software module has a corresponding path from the entry to the exit node of the module's control flow graph.

Computing Cyclomatic Complexity
Cyclomatic complexity has a foundation in graph theory and provides us with extremely useful software metric. Complexity is computed in one of the three ways:
- The number of regions of the flow graph corresponds to the cyclomatic complexity.
- Cyclomatic complexity, V(G), for a flow graph, G is defined as:
V(G)= E-N+2
where E is the number of flow graph edges and N is the number of flow graph nodes.
- Cyclomatic complexity, V(G) for a flow graph, G is also defined as:
V(G)= P+1
where P is the number of predicate nodes contained in the flow graph G.