Defect Testing in Software Engineering SE20

Defect testing Testing programs to establish the presence of system defects

Objectives To understand testing techniques that are geared to discover program faults To introduce guidelines for interface testing To understand specific approaches to object-oriented testing To understand the principles of CASE tool support for testing

Topics covered Defect testing Integration testing Object-oriented testing Testing workbenches

The testing process Component testing Testing of individual program components Usually the responsibility of the component developer (except sometimes for critical systems) Tests are derived from the developer’s experience Integration testing Testing of groups of components integrated to create a system or sub-system The responsibility of an independent testing team Tests are based on a system specification

Defect testing The goal of defect testing is to discover defects in programs A successful defect test is a test which causes a program to behave in an anomalous way Tests show the presence not the absence of defects

Only exhaustive testing can show a program is free from defects. However, exhaustive testing is impossible Tests should exercise a system's capabilities rather than its components Testing old capabilities is more important than testing new capabilities Testing typical situations is more important than boundary value cases Testing priorities

Test data Inputs which have been devised to test the system Test cases Inputs to test the system and the predicted outputs from these inputs if the system operates according to its specification Test data and test cases

Black-box testing An approach to testing where the program is considered as a ‘black-box’ The program test cases are based on the system specification Test planning can begin early in the software process

Equivalence partitioning Input data and output results often fall into different classes where all members of a class are related Each of these classes is an equivalence partition where the program behaves in an equivalent way for each class member Test cases should be chosen from each partition

Partition system inputs and outputs into ‘equivalence sets’ If input is a 5-digit integer between 10,000 and 99,999, equivalence partitions are <10,000, 10,000-99, 999 and > 10, 000 Choose test cases at the boundary of these sets 00000, 09999, 10000, 99999, 10001 Equivalence partitioning

Search routine specification procedure Search (Key : ELEM ; T: ELEM_ARRAY; Found : in out BOOLEAN; L: in out ELEM_INDEX) ; Pre-condition -- the array has at least one element T’FIRST <= T’LAST Post-condition -- the element is found and is referenced by L ( Found and T (L) = Key) or -- the element is not in the array ( not Found and not ( exists i, T’FIRST >= i <= T’LAST, T (i) = Key ))

Inputs which conform to the pre-conditions Inputs where a pre-condition does not hold Inputs where the key element is a member of the array Inputs where the key element is not a member of the array Search routine - input partitions

Testing guidelines (sequences) Test software with sequences which have only a single value Use sequences of different sizes in different tests Derive tests so that the first, middle and last elements of the sequence are accessed Test with sequences of zero length

Search routine - input partitions

Sometime called white-box testing Derivation of test cases according to program structure. Knowledge of the program is used to identify additional test cases Objective is to exercise all program statements (not all path combinations) Structural testing

Pre-conditions satisfied, key element in array Pre-conditions satisfied, key element not in array Pre-conditions unsatisfied, key element in array Pre-conditions unsatisfied, key element not in array Input array has a single value Input array has an even number of values Input array has an odd number of values Binary search - equiv. partitions

Binary search equiv. partitions

Path testing The objective of path testing is to ensure that the set of test cases is such that each path through the program is executed at least once The starting point for path testing is a program flow graph that shows nodes representing program decisions and arcs representing the flow of control Statements with conditions are therefore nodes in the flow graph

Describes the program control flow. Each branch is shown as a separate path and loops are shown by arrows looping back to the loop condition node Used as a basis for computing the cyclomatic complexity Cyclomatic complexity = Number of edges - Number of nodes +2 Program flow graphs

The number of tests to test all control statements equals the cyclomatic complexity Cyclomatic complexity equals number of conditions in a program Useful if used with care. Does not imply adequacy of testing. Although all paths are executed, all combinations of paths are not executed Cyclomatic complexity

1, 2, 3, 8, 9 1, 2, 3, 4, 6, 7, 2 1, 2, 3, 4, 5, 7, 2 1, 2, 3, 4, 6, 7, 2, 8, 9 Test cases should be derived so that all of these paths are executed A dynamic program analyser may be used to check that paths have been executed Independent paths

Integration testing Tests complete systems or subsystems composed of integrated components Integration testing should be black-box testing with tests derived from the specification Main difficulty is localising errors Incremental integration testing reduces this problem

Incremental integration testing

Approaches to integration testing Top-down testing Start with high-level system and integrate from the top-down replacing individual components by stubs where appropriate Bottom-up testing Integrate individual components in levels until the complete system is created In practice, most integration involves a combination of these strategies

Tetsing approaches Architectural validation Top-down integration testing is better at discovering errors in the system architecture System demonstration Top-down integration testing allows a limited demonstration at an early stage in the development Test implementation Often easier with bottom-up integration testing Test observation Problems with both approaches. Extra code may be required to observe tests

Takes place when modules or sub-systems are integrated to create larger systems Objectives are to detect faults due to interface errors or invalid assumptions about interfaces Particularly important for object-oriented development as objects are defined by their interfaces Interface testing

Interfaces types Parameter interfaces Data passed from one procedure to another Shared memory interfaces Block of memory is shared between procedures Procedural interfaces Sub-system encapsulates a set of procedures to be called by other sub-systems Message passing interfaces Sub-systems request services from other sub-systems

Interface errors Interface misuse A calling component calls another component and makes an error in its use of its interface e.g. parameters in the wrong order Interface misunderstanding A calling component embeds assumptions about the behaviour of the called component which are incorrect Timing errors The called and the calling component operate at different speeds and out-of-date information is accessed

Interface testing guidelines Design tests so that parameters to a called procedure are at the extreme ends of their ranges Always test pointer parameters with null pointers Design tests which cause the component to fail Use stress testing in message passing systems In shared memory systems, vary the order in which components are activated

Stress testing Exercises the system beyond its maximum design load. Stressing the system often causes defects to come to light Stressing the system test failure behaviour.. Systems should not fail catastrophically. Stress testing checks for unacceptable loss of service or data Particularly relevant to distributed systems which can exhibit severe degradation as a network becomes overloaded

The components to be tested are object classes that are instantiated as objects Larger grain than individual functions so approaches to white-box testing have to be extended No obvious ‘top’ to the system for top-down integration and testing Object-oriented testing

Testing levels Testing operations associated with objects Testing object classes Testing clusters of cooperating objects Testing the complete OO system

Object class testing Complete test coverage of a class involves Testing all operations associated with an object Setting and interrogating all object attributes Exercising the object in all possible states Inheritance makes it more difficult to design object class tests as the information to be tested is not localised

Weather station object interface Test cases are needed for all operations Use a state model to identify state transitions for testing Examples of testing sequences Shutdown  Waiting  Shutdown Waiting  Calibrating  Testing  Transmitting  Waiting Waiting  Collecting  Waiting  Summarising  Transmitting  Waiting

Object integration Levels of integration are less distinct in object-oriented systems Cluster testing is concerned with integrating and testing clusters of cooperating objects Identify clusters using knowledge of the operation of objects and the system features that are implemented by these clusters

Approaches to cluster testing Use-case or scenario testing Testing is based on a user interactions with the system Has the advantage that it tests system features as experienced by users Thread testing Tests the systems response to events as processing threads through the system Object interaction testing Tests sequences of object interactions that stop when an object operation does not call on services from another object

Scenario-based testing Identify scenarios from use-cases and supplement these with interaction diagrams that show the objects involved in the scenario Consider the scenario in the weather station system where a report is generated

Weather station testing Thread of methods executed CommsController:request  WeatherStation:report  WeatherData:summarise Inputs and outputs Input of report request with associated acknowledge and a final output of a report Can be tested by creating raw data and ensuring that it is summarised properly Use the same raw data to test the WeatherData object

Testing workbenches Testing is an expensive process phase. Testing workbenches provide a range of tools to reduce the time required and total testing costs Most testing workbenches are open systems because testing needs are organisation-specific Difficult to integrate with closed design and analysis workbenches

Tetsing workbench adaptation Scripts may be developed for user interface simulators and patterns for test data generators Test outputs may have to be prepared manually for comparison Special-purpose file comparators may be developed

Key points Test parts of a system which are commonly used rather than those which are rarely executed Equivalence partitions are sets of test cases where the program should behave in an equivalent way Black-box testing is based on the system specification Structural testing identifies test cases which cause all paths through the program to be executed

Key points Test coverage measures ensure that all statements have been executed at least once. Interface defects arise because of specification misreading, misunderstanding, errors or invalid timing assumptions To test object classes, test all operations, attributes and states Integrate object-oriented systems around clusters of objects

Defect Testing in Software Engineering SE20

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Defect Testing in Software Engineering SE20