Chapter 11, Testing

1. Chapter 11, Testing

2. Tell me how are you going to test the CALCULATOR

3. How to design test cases? • Test the functional requirement • Use case testing • Black box testing • Equivalence partition testing • Boundary testing • …. • Test the non-functional requirement • Performance testing • Acceptance testing • Installation testing • ….

4. Black box testing • Also known as functional testing. A software testing technique whereby the internal workings of the item being tested are not known by the tester. • For example, in a black box test on a software design the tester only knows the inputs and what the expected outcomes should be and not how the program arrives at those outputs. • The tester does not ever examine the programming code and does not need any further knowledge of the program other than its specifications. http://www.webopedia.com/TERM/B/Black_Box_Testing.html

5. Black box testing • The advantages of this type of testing include: • The test is unbiased because the designer and the tester are independent of each other. • The tester does not need knowledge of any specific programming languages. • The test is done from the point of view of the user, not the designer. • Test cases can be designed as soon as the specifications are complete. • The disadvantages of this type of testing include: • The test can be redundant if the software designer has already run a test case. • The test cases are difficult to design. • Testing every possible input stream is unrealistic because it would take a inordinate amount of time; therefore, many program paths will go untested.

6. White box testing • Also known as glass box, structural, clear box and open box testing. A software testing technique whereby explicit knowledge of the internal workings of the item being tested are used to select the test data. • Unlike black box testing, white box testing uses specific knowledge of programming code to examine outputs. The test is accurate only if the tester knows what the program is supposed to do. He or she can then see if the program diverges from its intended goal. • White box testing does not account for errors caused by omission, and all visible code must also be readable.

7. Black box testing and white box testing compared • White box testing is concerned only with testing the software product, it cannot guarantee that the complete specification has been implemented. • Black box testing is concerned only with testing the specification, it cannot guarantee that all parts of the implementation have been tested. • Thus black box testing is testing against the specification and will discover faults of omission, indicating that part of the specification has not been fulfilled. • White box testing is testing against the implementation and will discover faults of commission, indicating that part of the implementation is faulty. • In order to fully test a software product both black and white box testing are required. http://www.scism.sbu.ac.uk/law/Section5/chap3/s5c3p23.html

8. Black box testing and white box testing compared • White box testing is much more expensive than black box testing. It requires the source code to be produced before the tests can be planned and is much more laborious in the determination of suitable input data and the determination if the software is or is not correct. • The advice given is to start test planning with a black box test approach as soon as the specification is available. • White box planning should commence as soon as all black box tests have been successfully passed, with the production of flowgraphs and determination of paths. The paths should then be checked against the black box test plan and any additional required test runs determined and applied.

9. Quality assurance vs. quality control • The consequences of test failure at this stage may be very expensive. • A failure of a white box test may result in a change which requires all black box testing to be repeated and the re-determination of the white box paths. • The cheaper option is to regard the process of testing as one of quality assurance rather than quality control. The intention is that sufficient quality will be put into all previous design and production stages so that it can be expected that testing will confirm that there are very few faults present, quality assurance, rather than testing being relied upon to discover any faults in the software, quality control.

10. Testing: from the development process point of view Requirement Design& Implementation & Testing Final System Test case development & Testing Requirement Final System Design& Implementation

11. Terminology Types of errors Dealing with errors Component Testing Unit testing Integration testing Testing Strategy System testing Function testing Structure Testing Performance testing Acceptance testing Installation testing Outline

12. What is this? A failure? An error? A fault? Need to specifythe desired behavior first!

13. Terminology • Reliability: The measure of success with which the observed behavior of a system confirms to some specification of its behavior. • Software reliability is the probability that a software system will not cause system failure for a specified time under speciied conditions. • Failure: Any deviation of the observed behavior from the specified behavior. • Error: The system is in a state such that further processing by the system will lead to a failure. • Fault (Bug): The mechanical or algorithmic cause of an error. There are many different types of errors and different ways how we can deal with them.

14. How do we deal with Errors and Faults?

15. Verification?

16. Modular Redundancy?

17. Declaring the Bug as a Feature?

18. Patching?

19. Testing?

20. Faults in the Interface specification Mismatch between what the client needs and what the server offers Mismatch between requirements and implementation Algorithmic Faults Missing initialization Branching errors (too soon, too late) Missing test for nil Mechanical Faults (very hard to find) Documentation does not match actual conditions or operating procedures Errors Stress or overload errors Capacity or boundary errors Timing errors Throughput or performance errors Examples of Faults and Errors

21. Dealing with Errors • Verification: • Assumes hypothetical environment that does not match real environment • Proof might be buggy (omits important constraints; simply wrong) • Modular redundancy: • Expensive • Declaring a bug to be a “feature” • Bad practice • Patching • Slows down performance • Testing (this lecture) • Testing is never good enough

22. Another View on How to Deal with Errors • Error prevention (before the system is released): • Use good programming methodology to reduce complexity • Use version control to prevent inconsistent system • Apply verification to prevent algorithmic bugs • Error detection (while system is running): • Testing: Create failures in a planned way • Debugging: Start with an unplanned failures • Monitoring: Deliver information about state. Find performance bugs • Error recovery (recover from failure once the system is released): • Data base systems (atomic transactions) • Modular redundancy • Recovery blocks

23. Some Observations • It is impossible to completely test any nontrivial module or any system • Theoretical limitations: Halting problem • Practial limitations: Prohibitive in time and cost • Testing can only show the presence of bugs, not their absence (Dijkstra)

24. Testing takes creativity • Testing often viewed as dirty work. • To develop an effective test, one must have: • Detailed understanding of the system • Knowledge of the testing techniques • Skill to apply these techniques in an effective and efficient manner • Testing is done best by independent testers • We often develop a certain mental attitude that the program should in a certain way when in fact it does not. • Programmer often stick to the data set that makes the program work • "Don’t mess up my code!" • A program often does not work when tried by somebody else. • Don't let this be the end-user.

25. Testing Activities Requirements Analysis Document Subsystem Code Requirements Analysis Document Unit System Design Document T est Tested Subsystem User Manual Subsystem Code Unit T est Integration Tested Subsystem Functional Test Test Functioning System Integrated Subsystems Tested Subsystem Subsystem Code Unit T est All tests by developer

26. Testing Activities continued Client’s Understanding of Requirements User Environment Global Requirements Accepted System Validated System Functioning System Performance Acceptance Installation Test Test Test Usable System Tests by client Tests by developer User’s understanding System in Use Tests (?) by user

27. Test Cases • A test case is a set of input data and expected results that exercises a component with the purpose of causing failures and detecting faults. • A test case has five attributes.

28. Types of Testing • Unit Testing: • Individual subsystem • Carried out by developers • Goal: Confirm that subsystems is correctly coded and carries out the intended functionality • Integration Testing: • Groups of subsystems (collection of classes) and eventually the entire system • Carried out by developers • Goal: Test the interface among the subsystem

29. System Testing • System Testing: • The entire system • Carried out by developers • Goal: Determine if the system meets the requirements (functional and global) • Acceptance Testing: • Evaluates the system delivered by developers • Carried out by the client. May involve executing typical transactions on site on a trial basis • Goal: Demonstrate that the system meets customer requirements and is ready to use • Implementation (Coding) and testing go hand in hand

30. Unit Testing • Informal: • Incremental coding • Static Analysis: • Hand execution: Reading the source code • Walk-Through (informal presentation to others) • Code Inspection (formal presentation to others) • Automated Tools checking for • syntactic and semantic errors • departure from coding standards • Dynamic Analysis: • Black-box testing (Test the input/output behavior) • White-box testing (Test the internal logic of the subsystem or object) • Data-structure based testing (Data types determine test cases)

31. Black-box Testing • Focus: I/O behavior. If for any given input, we can predict the output, then the module passes the test. • Almost always impossible to generate all possible inputs ("test cases") • Goal: Reduce number of test cases by equivalence partitioning: • Divide input conditions into equivalence classes • Choose test cases for each equivalence class. (Example: If an object is supposed to accept a negative number, testing one negative number is enough)

32. Black-box Testing (Continued) • Selection of equivalence classes (No rules, only guidelines): • Input is valid across range of values. Select test cases from 3 equivalence classes: • Below the range • Within the range • Above the range • Input is valid if it is from a discrete set. Select test cases from 2 equivalence classes: • Valid discrete value • Invalid discrete value • Another solution to select only a limited amount of test cases: • Get knowledge about the inner workings of the unit being tested => white-box testing

33. Boundary Testing • A special case of equivalence testing • Focuses on the condition at the boundary of the equivalence classes. • The assumption behind boundary testing is that developers often overlook special cases at the boundary of the equivalence classes (e.g., 0, empty strings, year 2000).

34. White-box Testing • Focus: Thoroughness (Coverage). Every statement in the component is executed at least once. • Types of white-box testing • Path Testing • Loop Testing • State-Based testing

35. White-box Testing (Continued) • Path testing: • Make sure all paths in the program are executed • Loop Testing: • Cause execution of the loop to be skipped completely. (Exception: Repeat loops) • Loop to be executed exactly once • Loop to be executed more than once

36. Path testing • The assumption behind path testing is that, by exercising all possible paths through the code at least once, most faults will trigger failures. • The starting point for path testing is the flow graph.

38. Path testing (continue) • An example on book P. 456, 457,458 • Using graph theory, it can be shown that the minimum number of tests necessary to cover all edges is equal to the number of independent paths through the flow graph. CC = number of edges – number of nodes +2

39. For the example on book Number of Test cases = 18 – 14 +2 = 6

40. Loop Testing Example FindMean(float Mean, FILE ScoreFile) { SumOfScores = 0.0; NumberOfScores = 0; Mean = 0; Read(Scor eFile, Score); /*Read in and sum the scores*/ while (! EOF(ScoreFile) { if ( Score > 0.0 ) { SumOfScores = SumOfScores + Score; NumberOfScores++; } Read(ScoreFile, Score); } /* Compute the mean and print the result */ if (NumberOfScores > 0 ) { Mean = SumOfScores/NumberOfScores; printf("The mean score is %f \n", Mean); } else printf("No scores found in file\n"); }

41. 1 2 3 4 5 6 7 8 9 White-box Testing Example: Determining the Paths • FindMean (FILE ScoreFile) • { float SumOfScores = 0.0; • int NumberOfScores = 0; • float Mean=0.0; float Score; • Read(ScoreFile, Score); • while (! EOF(ScoreFile) { • if (Score > 0.0 ) { • SumOfScores = SumOfScores + Score; • NumberOfScores++; • } • Read(ScoreFile, Score); • } • /* Compute the mean and print the result */ • if (NumberOfScores > 0) { • Mean = SumOfScores / NumberOfScores; • printf(“ The mean score is %f\n”, Mean); • } else • printf (“No scores found in file\n”); • }

42. Constructing the Logic Flow Diagram

43. Finding the Test Cases Start 1 a (Covered by any data) 2 b (Data set must contain at least one value) 3 (Positive score) d e (Negative score) c 5 4 (Data set must h (Reached if either f or g f be empty) 6 e is reached) 7 j i (Total score > 0.0) (Total score < 0.0) 9 8 k l Exit

44. Test Cases • Test case 1 : ? (To execute loop exactly once) • Test case 2 : ? (To skip loop body) • Test case 3: ?,? (to execute loop more than once) • These 3 test cases cover all control flow paths

45. Test Cases testMethod( int y, int v){ int i=0; int x =y; for (i=0;i<v;i++){ if (x>0){ do A; } else { do B; } } System.out.println(“finish method”); }

46. White-box Testing: Potentially infinite number of paths have to be tested White-box testing often tests what is done, instead of what should be done Cannot detect missing use cases Black-box Testing: Potential combinatorical explosion of test cases (valid & invalid data) Often not clear whether the selected test cases uncover a particular error Does not discover extraneous use cases ("features") Both types of testing are needed White-box testing and black box testing are the extreme ends of a testing continuum. Any choice of test case lies in between and depends on the following: Number of possible logical paths Nature of input data Amount of computation Complexity of algorithms and data structures Comparison of White & Black-box Testing

47. 1. Select what has to be measured Analysis: Completeness of requirements Design: tested for cohesion Implementation: Code tests 2. Decide how the testing is done Code inspection Proofs (Design by Contract) Black-box, white box, Select integration testing strategy (big bang, bottom up, top down, sandwich) 3. Develop test cases A test case is a set of test data or situations that will be used to exercise the unit (code, module, system) being tested or about the attribute being measured 4. Create the test oracle An oracle contains of the predicted results for a set of test cases The test oracle has to be written down before the actual testing takes place The 4 Testing Steps

48. Use analysis knowledge about functional requirements (black-box testing): Use cases Expected input data Invalid input data Use design knowledge about system structure, algorithms, data structures (white-box testing): Control structures Test branches, loops, ... Data structures Test records fields, arrays, ... Use implementation knowledge about algorithms: Examples: Force division by zero Use sequence of test cases for interrupt handler Guidance for Test Case Selection

49. 1. Create unit tests as soon as object design is completed: Black-box test: Test the use cases & functional model White-box test: Test the dynamic model Data-structure test: Test the object model 2. Develop the test cases Goal: Find the minimal number of test cases to cover as many paths as possible 3. Cross-check the test cases to eliminate duplicates Don't waste your time! 4. Desk check your source code Reduces testing time 5. Create a test harness Test drivers and test stubs are needed for integration testing 6. Describe the test oracle Often the result of the first successfully executed test 7. Execute the test cases Don’t forget regression testing Re-execute test cases every time a change is made. 8. Compare the results of the test with the test oracle Automate as much as possible Unit-testing Heuristics

50. Integration Testing Strategy • The entire system is viewed as a collection of subsystems (sets of classes) determined during the system and object design. • The order in which the subsystems are selected for testing and integration determines the testing strategy • Big bang integration (Nonincremental) • Bottom up integration • Top down integration • Sandwich testing • Variations of the above • For the selection use the system decomposition from the System Design