Software Testing & Debugging

Software Testing & Debugging

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  Thanks to M8034@ Peter Lo 2006 1 Software Testing & Debugging 2 Software Testing Fundamentals ■ Software Testing is a critical element of software quality assurance and represents the ultimate review of specification, design and coding. ■ It is concerned with the actively identifying errors in software. ■ Testing is dynamic assessment of the software ◆ Sample input ◆ Actual outcome compare with expected outcome Testing Objectives ■ Software Testing is the process of exercising a program with the specific intent of finding errors prior to delivery to the end user. ■ It is the process of checking to see if software matches its specification for specific cases called Test Case. ■ A Good Test Case is one that has a high probability of finding undiscovered error. Testing vs. Debugging ■ Testing is different from debugging ■ Debugging is removal of defects in the software, a correction process ■ Testing is an assessment process ■ Testing consumes 40-50% of the development effort 3 4 Lecture 6 BSIT 6th Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  5 What can TestingShow? Errors Requirements Consistency Performance An indication of quality 6 Who Tests the Software? Independent TesterDeveloper Understands the system but, will test "gently" and, is driven by "delivery" Must learn about the system, but, will attempt to break it and, is driven by quality Testing Paradox ■ To gain confidence, a successful test is one that the software does as in the functional specs. ■ To reveal error, a successful test is one that finds an error. ■ In practice, a mixture of Defect-revealing and Correct- operation tests are used. Developer performs Constructive Actions Tester performs Destructive Actions ■ Two classes of input are provided to the test process: ◆ Software Configuration: includes Software Requirements Specification, Design Specification, and source code. ◆ Test Configuration: includes Test Plan and Procedure, any testing tools that are to be used, and test cases and their expected results. 7 8 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006Thanks to M8034 @ Peter Lo 2006
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  9 Necessary Conditions forTesting ■ A controlled/observed environment, because tests must be exactly reproducible ◆ Sample Input – test uses only small sample input (limitation) ◆ Predicted Result – the results of a test ideally should be predictable ■ Actual output must be able to compare with the expected output 10 Attributes of a “Good Test” ■ A good test has a high probability of finding an error. ◆ The tester must understand the software and attempt to develop a mental picture of how the software might fail. ■ A good test is not redundant. ◆ Testing time and resources are limited. ◆ There is no point in conducting a test that has the same purpose as another test. ■ A good test should be neither too simple nor too complex. ◆ Side effect of attempting to combine a series of tests into one test case is that this approach may mask errors. Attribute of 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 effective ■ Decomposability — Testing can be on different stages ■ Simplicity — Reduce complex architecture and logic to simplify tests ■ Stability — Few changes are requested during testing ■ Understandability — The purpose of the system is clear to the evaluator Software Testing Technique ■ White Box Testing, or Structure Testing is derived directly from the implementation of a module and able to test all the implemented code ■ Black Box Testing, or Functional Testing is able to test any functionality is missing from the implementation. Methods White-box Testing Black-box Testing 11 12 Strategies Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  13 White Box TestingTechnique (till slide 23) ■ White box testing is a test case design method that uses the control structure of the procedural design to derive test cases. ... our goal is to ensure that all statements and conditions have been executed at least once ... 14 White Box Testing Technique ■ White Box Testing of software is predicated on close examination of procedural detail. ■ Logical paths through the software are tested by providing test cases that exercise specific sets of conditions and / or loops. ■ The status of the program may be examined at various points to determine if the expected or asserted status corresponds to the actual status. Process of White Box Testing ■ Tests are derived from an examination of the source code for the modules of the program. ■ These are fed as input to the implementation, and the execution traces are used to determine if there is sufficient coverage of the program source code Benefit of White Box Testing ■ Using white box testing methods, the software engineer can derive test cases that: ◆ Guarantee that all independent paths within a module have been exercised at least once; ◆ Exercise all logical decisions on their true or false sides; ◆ Execute all loops at their boundaries and within their operational bounds ; and ◆ Exercise internal data structures to ensure their validity. 15 16 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  17 Exhaustive Testing ■ Thereare 1014 possible paths! If we execute one test per millisecond, it would take 3,170 years to test this program!! loop < 20 X Selective Testing loop < 20 X Selected path Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 18
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  19 Condition Testing ■ Simplecondition is a Boolean variable or relational expression (>, <) ■ Condition testing is a test case design method that exercises the logical conditions contained in a program module, and therefore focuses on testing each condition in the program. ■ (type of white box testing) Data Flow Testing ■ The Data flow testing method selects test paths of a program according to the locations of definitions and uses of variables in the program 36 Loop Testing ■ Loop testing is a white-box testing technique that focuses exclusively on the validity of loop constructs ■ Four classes of loops: 1. Simple loops 2. Concatenated loops 3. Nested loops 4. Unstructured loops 20 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 21
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  22 Test Cases forSimple Loops ■ Where n is the maximum number of allowable passes through the loop: ◆ Skip the loop entirely ◆ Only one pass through the loop ◆ Two passes through the loop ◆ m passes through the loop where m<n ◆ n-1, n, n+1 passes through the loop Simple loop 23 Test Cases for Nested Loops ■ Start at the innermost loops. Set all other loops to minimum values ■ Conduct simple loop tests for the innermost loop while holding the outer loops at their minimum iteration parameter values. Add other tests for out-of -range or excluded values ■ Work outward, conducting tests for the next loop but keeping all other outer loops at minimum values and other nested loops to "typical" values ■ Continue until all loops have been tested Nested Loops Thanks to M8034 @ Peter Lo 2006Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  24 Black Box Testing ■Black Box Testing focus on the functional requirements of the software, i.e. derives sets of input conditions that will fully exercise all functional requirements for a program. Requirements EventsInput Output 25 Black Box Testing ■ Black box testing attempts to find errors in the following categories: ◆ Incorrect or missing functions ◆ Interface errors ◆ Errors in data structures or external databases access ◆ Performance errors ◆ Initialization and termination errors. Process of Black Box Testing Random Testing ■ Input is given at random and submitted to the program and corresponding output is then compared. 26 27 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  28 Comparison Testing ■ Allthe versions are executed in parallel with a real- time comparison of results to ensure consistency. ◆ If the output from each version is the same, then it is assumed that all implementations are correct. ◆ If the output is different, each of the applications is investigated to determine if a defect in one or more versions is responsible for the difference. 29 Automated Testing Tools ■ CodeAuditors ■ Assertion Processors ■ Test File Generators ■ Test Data Generators ■ Test Verifiers ■ Output Comparators ■ Other name = test automation tools, can be in both static and dynamic, explore yourself Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  30 Testing Strategy Unit Test ■A testing strategy must always incorporate test planning, test case design, text execution, and the resultant data collection and evaluation Integration Test Validation Test System Test 31 Test Case Design "Bugs lurk in corners and congregate at boundaries ..." Boris Beizer OBJECTIVE CRITERIA CONSTRAINT to uncover errors in a complete manner with a minimum of effort and time Verification and Validation ■ Verification – It confirms software specifications ◆ Are we building the project right? ■ Validation – it confirms software is according to customer’s expectations. ◆ Are we building the right product? Generic Characteristics of Software Testing Strategies ■ Testing begins at the module level and works toward the integration of the entire system ■ Different testing techniques are appropriate at different points in time ■ Testing is conducted by the software developer and an Independent Test Group (ITG) ■ Debugging must be accommodated in any testing strategy 32 33 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  M8034 @ PeterLo 2006 65 Software Testing Strategy 35 Software Testing Strategy ■ A strategy for software testing moves outward along the spiral. ◆ Unit Testing: Concentrates on each unit of the software as implemented in the source code. ◆ Integration Testing: Focus on the design and the construction of the software architecture. ◆ Validation Testing: Requirements established as part of software requirement analysis are validated against the software that has been constructed. ◆ System Testing: The software and other system elements are tested as a whole. M8034 @ Peter Lo 2006 67 Testing Direction Software Testing Direction ■ Unit Tests ◆ Focuses on each module and makes heavy use of white box testing ■ Integration Tests ◆ Focuses on the design and construction of software architecture; black box testing is most prevalent with limited white box testing. ■ High-order Tests ◆ Conduct validation and system tests. Makes use of black box testing exclusively (such as Validation Test, System Test, Alpha and Beta Test, and other Specialized Testing). 37 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  38 Unit Testing Module to be Tested TestCases Results Software Engineer 39 Unit Testing ■ Unit testing focuses on the results from coding. ■ Each module is tested in turn and in isolation from the others. ■ Uses white-box techniques. Interface Local Data Structures Boundary Conditions Independent Paths Error Handling Paths Module to be Tested Test Cases Unit Testing Procedures ■ Module is not a stand-alone program, software must be developed for each unit test. ■ A driver is a program that accepts test case data, passes such data to the module, and prints the relevant results. ■ Stubs serve to replace modules that are subordinate the module to be tested. ■ A stub or "dummy subprogram" uses the subordinate module's interface, may do nominal data manipulation, prints verification of entry, and returns. ■ Drivers and stubs also represent overhead 40 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  41 42 Integration Testing ■ Atechnique for constructing the program structure while at the same time conducting tests to uncover tests to uncover errors associated with interfacing ■ Objective is combining unit-tested modules and build a program structure that has been dictated by design. ■ Integration testing should be done incrementally. ■ It can be done top-down, bottom-up or in bi-directional. 43 76Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 M8034 @ Peter Lo 2006 77 Example ■ For the program structure, the following test cases may be derived if top-down integration is conducted: ◆ Test case 1: Modules A and B are integrated ◆ Test case 2: Modules A, B and C are integrated ◆ Test case 3: Modules A., B, C and D are integrated (etc.) Validation Testing ■ Ensuring software functions can be reasonably expected by the customer. ■ Achieve through a series of black tests that demonstrate conformity with requirements. ■ A test plan outlines the classes of tests to be conducted, and a test procedure defines specific test cases that will be used in an attempt to uncover errors in conformity with requirements. ■ Validation testing begins, driven by the validation criteria that were elicited during requirement capture. ■ A series of acceptance tests are conducted with the end users System Testing ■ System testing is a series of different tests whose primary purpose is to fully exercise the computer-based system. ■ System testing focuses on those from system engineering. ■ Test the entire computer-based system. ■ One main concern is the interfaces between software, hardware and human components. ■ Kind of System Testing ◆ Recovery ◆ Security ◆ Stress ◆ Performance
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  85 Recovery Testing ■ Asystem test that forces software to fail in a variety of ways and verifies that recovery is properly performed. ■ If recovery is automatic, re-initialization, check- pointing mechanisms, data recovery, and restart are each evaluated for correctness. ■ If recovery is manual, the mean time to repair is evaluated to determine whether it is within acceptable limits. 86 Security Testing ■ Security testing attempts to verify that protection mechanisms built into a system will in fact protect it from improper penetration. ■ Particularly important to a computer-based system that manages sensitive information or is capable of causing actions that can improperly harm individuals when targeted. Stress Testing ■ Stress Testing is designed to confront programs with abnormal situations where unusual quantity frequency, or volume of resources are demanded ■ A variation is called sensitivity testing; ◆ Attempts to uncover data combinations within valid input classes that may cause instability or improper processing Performance Testing ■ Test the run-time performance of software within the context of an integrated system. ■ Extra instrumentation can monitor execution intervals, log events as they occur, and sample machine states on a regular basis ■ Use of instrumentation can uncover situations that lead to degradation and possible system failure 87 88 Thanks to M8034 @ Peter Lo 2006Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  89 Debugging ■ Debugging willbe the process that results in the removal of the error after the execution of a test case. ■ Its objective is to remove the defects uncovered by tests. ■ Because the cause may not be directly linked to the symptom, it may be necessary to enumerate hypotheses explicitly and then design new test cases to allow confirmation or rejection of the hypothesized cause. 90 The Debugging Process Test Cases Results Debugging Identified Causes Corrections Regression Tests New test Cases Suspected Causes What is Bug? ■ A bug is a part of a program that, if executed in the right state, will cause the system to deviate from its specification (or cause the system to deviate from the behavior desired by the user). Characteristics of Bugs ■ The symptom and the cause may be geographically remote ■ The symptom may disappear when another error is corrected ■ The symptom may actually be caused by non-errors ■ The symptom may be caused by a human error that is not easily traced ■ It may be difficult to accurately reproduce input conditions ■ The symptom may be intermittent. This is particularly common in embedded systems that couple hardware and software inextricably ■ The symptom may be due to causes that are distributed across a number of tasks running on different processors 91 92 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  93 Debugging Techniques Brute Force/ Testing Backtracking Cause Elimination 94 Debugging Approaches – Brute Force ■ Probably the most common and least efficient method for isolating the cause of a software error. ■ The program is loaded with run-time traces, and WRITE statements, and hopefully some information will be produced that will indicated a clue to the cause of an error. Debugging Approaches – Backtracking ■ Fairly common in small programs. ■ Starting from where the symptom has been uncovered, backtrack manually until the site of the cause is found. ■ Unfortunately, as the number of source code lines increases, the number of potential backward paths may become unmanageably large. Debugging Approaches – Cause Elimination ■ Data related to the error occurrence is organized to isolate potential causes. ■ A "cause hypothesis" is devised and the above data are used to prove or disapprove the hypothesis. ■ Alternatively, a list of all possible causes is developed and tests are conducted to eliminate each. ■ If the initial tests indicate that a particular cause hypothesis shows promise, the data are refined in a attempt to isolate the bug. 95 96 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006
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  101 Debugging Effort Time required todiagnose the symptom and determine the cause Time required to correct the error and conduct regression tests 102 Consequences of Bugs infectious damage catastrophic extreme serious disturbing mild annoying Bug Type Bug Categories: function-related bugs, system-related bugs, data bugs, coding bugs, design bugs, documentation bugs, standards violations, etc. Debugging Tools ■ Debugging compilers ■ Dynamic debugging aides ("tracers") ■ Automatic test case generators ■ Memory dumps Debugging: Final Thoughts ■ Don't run off half-cocked, think about the symptom you're seeing. ■ Use tools (e.g., dynamic debugger) to gain more insight. ■ If at an impasse, get help from someone else. ■ Be absolutely sure to conduct regression tests when you do "fix" the bug. 103 104 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006 Thanks to M8034 @ Peter Lo 2006