1. Software Engineering Software Testing Slide 1 Software Engineering Software Testing The material is this presentation is based on the following references and other internet resources: Ian Sommerville, Software Engineering (Seventh Edition), Addison-Wesley, 2004. Roger Pressman, Software Engineering, A Practitioner Approach, 6th ed., McGraw Hill, 2005.

2. Software Engineering Software Testing Slide 2 Objectives To discuss the distinctions between validation testing and defect testing To describe the principles of system and component testing To describe strategies for generating system test cases To understand the essential characteristics of tool used for test automation

3. Software Engineering Software Testing Slide 3 Topics covered System testing Component testing Test case design Test automation

4. Software Engineering Software Testing Slide 4 Testability Operability—it operates cleanly Observability—the results of each test case are readily observed Controllability—the degree to which testing can be automated and optimized Decomposability—testing can be targeted Simplicity—reduce complex architecture and logic to simplify tests Stability—few changes are requested during testing Understandability—of the design

5. Software Engineering Software Testing Slide 5 What is a “Good” Test? A good test has a high probability of finding an error A good test has a high probability of finding an error A good test is not redundant. A good test is not redundant. A good test should be “best of breed” A good test should be “best of breed” A good test should be neither too simple nor too complex A good test should be neither too simple nor too complex A good test has a high probability of finding an error A good test has a high probability of finding an error A good test is not redundant. A good test is not redundant. A good test should be “best of breed” A good test should be “best of breed” A good test should be neither too simple nor too complex A good test should be neither too simple nor too complex

6. Software Engineering Software Testing Slide 6 What Testing Shows errors requirements conformance performance an indication of quality

7. Software Engineering Software Testing Slide 7 Who Tests the Software? Developer Understands the system but, will test "gently“ and, is driven by "delivery" independent tester Must learn about the system, but, will attempt to break it and, is driven by quality

8. Software Engineering Software Testing Slide 8 Testing phases

9. Software Engineering Software Testing Slide 9 Testing Strategy We begin by ‘testing-in-the-small’ and move toward ‘testing- in-the-large’ For conventional software –The module (component) is our initial focus –Integration of modules follows For OO software –our focus when “testing in the small” changes from an individual module (the conventional view) to an OO class that encompasses attributes and operations and implies communication and collaboration

10. Software Engineering Software Testing Slide 10 Testing Strategy unit test integration test system test validation test

11. Software Engineering Software Testing Slide 11 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. System 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.

12. Software Engineering Software Testing Slide 12 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

13. Software Engineering Software Testing Slide 13 Testing process goals Validation testing –To demonstrate to the developer and the system customer that the software meets its requirements. –A successful test shows that the system operates as intended. Defect testing –To discover faults or defects in the software where its behavior is incorrect or not in conformance with its specification. –A successful test is a test that makes the system perform incorrectly and so exposes a defect in the system.

14. Software Engineering Software Testing Slide 14 The software testing process

15. Software Engineering Software Testing Slide 15 Testing policies Only exhaustive testing can show a program is free from defects. However, exhaustive testing is impossible, Testing policies define the approach to be used in selecting system tests: –All functions accessed through menus should be tested; –Combinations of functions accessed through the same menu should be tested; –Where user input is required, all functions must be tested with correct and incorrect input.

16. Software Engineering Software Testing Slide 16 Exhaustive Testing loop < 20 X

17. Software Engineering Software Testing Slide 17 Selective Testing loop < 20 X Selected path

18. Software Engineering Software Testing Slide 18 Component testing Component or unit testing is the process of testing individual components in isolation. It is a defect testing process. Components may be: –Individual functions or methods within an object; –Object classes with several attributes and methods; –Composite components with defined interfaces used to access their functionality.

19. Software Engineering Software Testing Slide 19 Unit Testing test cases results Software engineer module to be tested

20. Software Engineering Software Testing Slide 20 Unit Testing module to be tested Interface local data structures boundary conditions independent paths error handling paths test cases results

21. Software Engineering Software Testing Slide 21 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.

22. Software Engineering Software Testing Slide 22 Interface testing 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.

23. Software Engineering Software Testing Slide 23 Interface testing

24. Software Engineering Software Testing Slide 24 Interface types Parameter interfaces –Data passed from one procedure to another. Shared memory interfaces –Block of memory is shared between procedures or functions. 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

25. Software Engineering Software Testing Slide 25 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.

26. Software Engineering Software Testing Slide 26 Integration Testing Strategies Options: the “big bang” approach an incremental construction strategy

27. Software Engineering Software Testing Slide 27 Integration testing Involves building a system from its components and testing it for problems that arise from component interactions. Top-down integration –Develop the skeleton of the system and populate it with components. Bottom-up integration –Integrate infrastructure components then add functional components. To simplify error localisation, systems should be incrementally integrated.

28. Software Engineering Software Testing Slide 28 Top Down Integration A B C DE FG top module is tested with stubs stubs are replaced one at a time, "depth first" as new modules are integrated, some subset of tests is re-run

29. Software Engineering Software Testing Slide 29 Bottom-Up Integration drivers are replaced one at a time, "depth first" worker modules are grouped into builds and integrated A B C DE FG cluster

30. Software Engineering Software Testing Slide 30 Sandwich Testing Top modules are tested with stubs Worker modules are grouped into builds and integrated A B C DE FG cluster

31. Software Engineering Software Testing Slide 31 System testing Involves integrating components to create a system or sub-system. May involve testing an increment to be delivered to the customer. Two phases: –Integration testing - the test team have access to the system source code. The system is tested as components are integrated. –Release testing - the test team test the complete system to be delivered as a black-box.

32. Software Engineering Software Testing Slide 32 Object-Oriented Testing begins by evaluating the correctness and consistency of the OOA and OOD models testing strategy changes –the concept of the ‘unit’ broadens due to encapsulation –integration focuses on classes and their execution across a ‘thread’ or in the context of a usage scenario –validation uses conventional black box methods

33. Software Engineering Software Testing Slide 33 OOT Strategy class testing is the equivalent of unit testing –operations within the class are tested –the state behavior of the class is examined integration applied three different strategies –thread-based testing—integrates the set of classes required to respond to one input or event –use-based testing—integrates the set of classes required to respond to one use case –cluster testing—integrates the set of classes required to demonstrate one collaboration

34. Software Engineering Software Testing Slide 34 Incremental integration testing

35. Software Engineering Software Testing Slide 35 Testing 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.

36. Software Engineering Software Testing Slide 36 Black-box testing

37. Software Engineering Software Testing Slide 37 Testing guidelines Testing guidelines are hints for the testing team to help them choose tests that will reveal defects in the system –Choose inputs that force the system to generate all error messages; –Design inputs that cause buffers to overflow; –Repeat the same input or input series several times; –Force invalid outputs to be generated; –Force computation results to be too large or too small.

38. Software Engineering Software Testing Slide 38 Use cases Use cases can be a basis for deriving the tests for a system. They help identify operations to be tested and help design the required test cases. From an associated sequence diagram, the inputs and outputs to be created for the tests can be identified.

39. Software Engineering Software Testing Slide 39 Test case design Involves designing the test cases (inputs and outputs) used to test the system. The goal of test case design is to create a set of tests that are effective in validation and defect testing. Design approaches: –Requirements-based testing; –Partition testing; –Structural testing.

40. Software Engineering Software Testing Slide 40 OOT—Test Case Design Berard [BER93] proposes the following approach: 1.Each test case should be uniquely identified and should be explicitly associated with the class to be tested, 2.The purpose of the test should be stated, 3.A list of testing steps should be developed for each test and should contain [BER94]: a list of specified states for the object that is to be tested b. a list of messages and operations that will be exercised as a consequence of the test c. a list of exceptions that may occur as the object is tested d. a list of external conditions (i.e., changes in the environment external to the software that must exist in order to properly conduct the test) e. supplementary information that will aid in understanding or implementing the test.

41. Software Engineering Software Testing Slide 41 Test Case Design OBJECTIVE to uncover errors CRITERIA in a complete manner CONSTRAINT with a minimum of effort and time

42. Software Engineering Software Testing Slide 42 Requirements based testing A general principle of requirements engineering is that requirements should be testable. Requirements-based testing is a validation testing technique where you consider each requirement and derive a set of tests for that requirement.

43. Software Engineering Software Testing Slide 43 Software Testing Methods Strategies white-box methods black-box methods

44. Software Engineering Software Testing Slide 44 Black-Box Testing requirements events input output

45. Software Engineering Software Testing Slide 45 Black-Box Testing How is functional validity tested? How is system behavior and performance tested? What classes of input will make good test cases? Is the system particularly sensitive to certain input values? How are the boundaries of a data class isolated? What data rates and data volume can the system tolerate? What effect will specific combinations of data have on system operation?

46. Software Engineering Software Testing Slide 46 Equivalence Partitioning userqueries mousepicks outputformats prompts FKinput data

47. Software Engineering Software Testing Slide 47 Boundary Value Analysis userqueries mousepicks outputformats prompts FKinput data outputdomain input domain

48. Software Engineering Software Testing Slide 48 Partition testing 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 or domain where the program behaves in an equivalent way for each class member. Test cases should be chosen from each partition.

49. Software Engineering Software Testing Slide 49 Equivalence partitioning

50. Software Engineering Software Testing Slide 50 Equivalence partitions

51. Software Engineering Software Testing Slide 51 Search routine specification procedure Search (Key : ELEM ; T: SEQ of ELEM; Found : in out BOOLEAN; L: in out ELEM_INDEX) ; Pre-condition -- the sequence 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 ))

52. Software Engineering Software Testing Slide 52 Search routine - input partitions 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.

53. Software Engineering Software Testing Slide 53 OOT Methods: Random Testing Random testing –identify operations applicable to a class –define constraints on their use –identify a minimum test sequence –generate a variety of random (but valid) test sequences

54. Software Engineering Software Testing Slide 54 OOT Methods: Partition Testing Partition Testing –reduces the number of test cases required to test a class in much the same way as equivalence partitioning for conventional software –state-based partitioning categorize and test operations based on their ability to change the state of a class –attribute-based partitioning categorize and test operations based on the attributes that they use –category-based partitioning categorize and test operations based on the generic function each performs

55. Software Engineering Software Testing Slide 55 Sample Equivalence Classes Valid dataValid data –user supplied commands –responses to system prompts –file names computational datacomputational data physical parametersphysical parameters bounding valuesbounding values initiation valuesinitiation values output data formattingoutput data formatting responses to error messagesresponses to error messages graphical data (e.g., mouse picks)graphical data (e.g., mouse picks) Invalid dataInvalid data –data outside bounds of the program –physically impossible data –proper value supplied in wrong place

56. Software Engineering Software Testing Slide 56 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.

57. Software Engineering Software Testing Slide 57 Search routine - input partitions

58. Software Engineering Software Testing Slide 58 Structural testing 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).

59. Software Engineering Software Testing Slide 59 Structural testing

60. Software Engineering Software Testing Slide 60 Binary search - equiv. partitions 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.

61. Software Engineering Software Testing Slide 61 Binary search equiv. partitions

62. Software Engineering Software Testing Slide 62 Binary search - test cases

63. Software Engineering Software Testing Slide 63 White-Box Testing... our goal is to ensure that all statements and conditions have been executed at least once...

64. Software Engineering Software Testing Slide 64 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.

65. Software Engineering Software Testing Slide 65 Binary search flow graph

66. Software Engineering Software Testing Slide 66 Independent paths 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 14 1, 2, 3, 4, 5, 14 1, 2, 3, 4, 5, 6, 7, 11, 12, 5, … 1, 2, 3, 4, 6, 7, 2, 11, 13, 5, … 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

67. Software Engineering Software Testing Slide 67 Why Cover? logic errors and incorrect assumptions are inversely proportional to a path's execution probability we often believe that a path is not likely to be executed; in fact, reality is often counter intuitive typographical errors are random; it's likely that untested paths will contain some

68. Software Engineering Software Testing Slide 68 Basis Path Testing First, we compute the cyclomatic complexity: or number of enclosed areas + 1 In this case, V(G) = 4 number of simple decisions + 1

69. Software Engineering Software Testing Slide 69 Cyclomatic Complexity A number of industry studies have indicated that the higher V(G), the higher the probability or errors. V(G) modules modules in this range are more error prone

70. Software Engineering Software Testing Slide 70 Basis Path Testing Next, we derive the independent paths: Since V(G) = 4, there are four paths Path 1: 1,2,3,6,7,8 Path 2: 1,2,3,5,7,8 Path 3: 1,2,4,7,8 Path 4: 1,2,4,7,2,4,...7,8 Finally, we derive test cases to exercise these paths. 1 2 3 4 56 7 8

71. Software Engineering Software Testing Slide 71 Basis Path Testing Notes you don't need a flow chart, but the picture will help when you trace program paths count each simple logical test, compound tests count as 2 or more basis path testing should be applied to critical modules

72. Software Engineering Software Testing Slide 72 Control Structure Testing Condition testing — a test case design method that exercises the logical conditions contained in a program module Data flow testing — selects test paths of a program according to the locations of definitions and uses of variables in the program

73. Software Engineering Software Testing Slide 73 Loop Testing NestedLoops Concatenated Loops Loops Unstructured Loops Simpleloop

74. Software Engineering Software Testing Slide 74 Loop Testing: Simple Loops Minimum conditions—Simple LoopsMinimum conditions—Simple Loops skip the loop entirely only one pass through the loop two passes through the loop m passes through the loop m < n (n-1), n, and (n+1) passes through the loop where n is the maximum number of allowable passes

75. Software Engineering Software Testing Slide 75 Loop Testing: Nested Loops Nested Loops Start at the innermost loop. Set all outer loops to their minimum iteration parameter values. Test the min+1, typical, max-1 and max for the innermost loop, while holding the outer loops at their minimum values. Move out one loop and set it up as in step 2, holding all other loops at typical values. Continue this step until the outermost loop has been tested.

76. Software Engineering Software Testing Slide 76 Loop Testing: Nested Loops (cont.) Concatenated Loops If the loops are independent of one another then treat each as a simple loop else* treat as nested loops endif*

77. Software Engineering Software Testing Slide 77 Release testing The process of testing a release of a system that will be distributed to customers. Primary goal is to increase the supplier’s confidence that the system meets its requirements. Release testing is usually black-box or functional testing –Based on the system specification only; –Testers do not have knowledge of the system implementation.

78. Software Engineering Software Testing Slide 78 Performance testing Part of release testing may involve testing the emergent properties of a system, such as performance and reliability. Performance tests usually involve planning a series of tests where the load is steadily increased until the system performance becomes unacceptable.

79. Software Engineering Software Testing Slide 79 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. Stress testing is particularly relevant to distributed systems that can exhibit severe degradation as a network becomes overloaded.

80. Software Engineering Software Testing Slide 80 Test automation Testing is an expensive process phase. Testing workbenches provide a range of tools to reduce the time required and total testing costs. Systems such as Junit support the automatic execution of tests. Most testing workbenches are open systems because testing needs are organisation-specific. They are sometimes difficult to integrate with closed design and analysis workbenches.

81. Software Engineering Software Testing Slide 81 A testing workbench

82. Software Engineering Software Testing Slide 82 Key points Testing can show the presence of faults in a system; it cannot prove there are no remaining faults. Component developers are responsible for component testing; system testing is the responsibility of a separate team. Integration testing is testing increments of the system; release testing involves testing a system to be released to a customer. Use experience and guidelines to design test cases in defect testing.

83. Software Engineering Software Testing Slide 83 Key points Interface testing is designed to discover defects in the interfaces of composite components. Equivalence partitioning is a way of discovering test cases - all cases in a partition should behave in the same way. Structural analysis relies on analysing a program and deriving tests from this analysis. Test automation reduces testing costs by supporting the test process with a range of software tools.