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Software Engineering – Software Testing Strategies STRATEGIC APPROACH Testing is a set of activities that can be planned in advance and conducted systematically. Many strategies exist, all follow these generic characteristics: To perform testing, a software team should conduct effective formal technical reviews. This eliminates errors before testing commences. Testing begins at the component level and works outward toward the integration of the entire computer-based system. Different testing techniques are appropriate at different points of time. Testing is conducted by the developer of the software and (for large projects) an independent test group. Testing and debugging are different activities, but debugging must be accommodated in any testing strategy. Software Engineering – Software Testing Strategies VERIFICATION VS. VALIDATION Verification refers to the set of activities the ensures that software correctly implements a specific function. Validation refers to a different set of activities that ensures that the software that has been built is traceable to customer requirements. Verification: Are we building the product right? Validation: Are we building the right product? Software Engineering – Software Testing Strategies ORGANIZING TESTING “Optimism is the occupational hazard of programming; testing is the treatment.” Kent Beck “The first mistake that people make is thinking that the testing team is responsible for assuring quality” Software Engineering – Software Testing Strategies ORGANIZING TESTING Software testing may be viewed as a spiral process: Software Engineering – Software Testing Strategies ORGANIZING TESTING Software Testing Steps Software Engineering – Software Testing Strategies WHEN IS TESTING COMPLETE? How do you know when you are done testing? There is no definitive answer to this question. Many possible answers: You are never done testing. You are done testing when you run out of money or time. Depends upon the certainty of failure you desire. Software Engineering – Software Testing Strategies STRATEGIC ISSUES The following issues must be addressed if a successful software testing strategy is to be implemented: Specify product requirements in a quantifiable manner long before testing commences. State testing objectives explicitly. – test coverage, mean time to failure, cost to find and fix defects, remaining defect density or frequency of occurrence Understand the users of the software and develop a profile for each user category. Build robust software that is designed to test itself. Use effective formal technical reviews prior to testing. Conduct formal technical reviews to assess the test strategy and test cases themselves. Develop a continuous improvement approach for the testing process. Software Engineering – Software Testing Strategies TEST STRATEGIES Unit Testing – focuses verification effort on the smallest unit of software design. (The component or module) Considerations: The module interface is tested to ensure that information properly flows into and out of the program unit under test. Local data structures are examined to ensure that data stored temporarily maintains its integrity during all steps in an algorithm’s execution. All independent paths through the control structure are exercised to ensure that all statements in a module have been executed at least once. Boundary conditions are tested to ensure that the module operates properly. Error handling paths are tested. Software Engineering – Software Testing Strategies TEST STRATEGIES Start testing data flow across the module interface. Exercise all local data structures, test impact on global structures. Common errors include: misunderstood or incorrect arithmetic precedence mixed mode operations incorrect initialization precision inaccuracy incorrect symbolic representation of an expression Software Engineering – Software Testing Strategies TEST STRATEGIES UNIT TESTING PROCEDURES Unit testing is normally considered as an adjunct to the coding step. Design of tests can be done before coding begins (Agile programming) Software Engineering – Software Testing Strategies TEST STRATEGIES UNIT TESTING PROCEDURES Software Engineering – Software Testing Strategies TEST STRATEGIES UNIT TESTING PROCEDURES Since each component is not a stand alone program, a bit of work must be done to perform the test. Create a driver, usually a main program, that accepts test case data and passes it ot the component to be tested. It also may print relevant results. Stubs replace modules that may not be coded and are subordinate to the component to be tested. A stub may do minimum data manipulation , provides verification of entry, and returns control to the module undergoing testing. Software Engineering – Software Testing Strategies TEST STRATEGIES UNIT TESTING PROCEDURES Unit testing is simpler when modules are highly cohesive. Software Engineering – Software Testing Strategies TEST STRATEGIES INTERGRATION TESTING Why is unit testing not enough? Data can be lost across an interface. One module can have an inadvertent effect on another. Global data structures can present problems Individually acceptable imprecision may become magnified. Resource issues. Software Engineering – Software Testing Strategies TEST STRATEGIES INTERGRATION TESTING Integration testing is a systematic technique for constructing the software architecture while at the same time conducting tests to uncover errors associated with interfacing. The objective is to take unit tested components and build a program structure that has been dictated by design. Software Engineering – Software Testing Strategies TEST STRATEGIES INTERGRATION TESTING There is a tendency to attempt nonincremental integration – construct the whole program via a “big-bang” approach. Thus to combine all components at once and test it as an entire program. Software Engineering – Software Testing Strategies TEST STRATEGIES INTERGRATION TESTING Top Down Integration is an incremental approach to construction of the software architecture. Modules are integrated by moving downward through the control hierarchy, beginning with the main control module. Modules subordinate to the main control module are incorporated into the structure in either a depth first or breath first manner. Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING The integration process is preformed in five steps: 1. The main control module is used as a test driver, and stubs are substituted for all components directly subordinate to the main control module. 2. Depending on the integration approach selected (i.e. depth or breath first), subordinate stubs are replaced one at a time with actual components. 3. Tests are conducted as each component is integrated. 4. On completion of each set of tests, another stub is replaced with the real component. 5. Regression testing may be conducted to ensure that new errors have not been introduced. Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING Verifies major control or decision points early Problems exist however: When processing at low levels in the hierarchy is required to test upper levels stubs replace low-levels in the hierarchy, therefore no significant data can flow upward in the program structure. Three options: 1. delay many tests until stubs are replaced with actual models 2. develop stubs that perform limited functions that simulate the actual module 3. integrate the software from the bottom of the hierarchy upward 1. The first method causes us to lose control over specific tests and specific modules. Thus leading to difficulty determining the cause of errors and violates the nature of the top down approach. 2. The second method is workable, but leads to significant overhead. 3. The third approach is called bottom-up testing, to be covered shortly. Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING Bottom Up Integration Begins construction and testing with atomic modules. Since all subordinates are always available, there is no need for stubs. Bottom up integration follows the following steps: 1. Low-level components are combined into clusters that perform a specific software subfunction. 2. A driver (control program for testing) is written to coordinate test cases input and output. 3. The cluster is tested. 4. Drivers are removed and clusters are combined moving upward in the program structure. One major disadvantage of bottom up integration is that the program as an entity does not exist until the last module is added. Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING Bottom Up Integration Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING Regression Testing Each time a new module is added, the software changes. These changes may cause problems with functions that previously worked. Therefore, we must re-execute some subset of tests that were already conducted to ensure that changes have not propagated unintended side effects. Any time you test, if successful you will find errors. When those errors are corrected, software changes. Therefore, regression testing must be performed in order to ensure that those changes did not propagate unintended side effects. Regression tests may be conducted manually – I do not recommend this. Software Engineering – Software Testing Strategies TEST STRATEGIES - INTERGRATION TESTING Integration Test Documentation The overall plan for integration of the software and a description of specific tests are documented in a Test Specification. The document contains: a test plan a test procedure is a work product of the software process becomes a part of the software configuration A test plan describes the overall strategy of integration. Testing is divided into phases and builds that address specific functional and behavioral characteristics of the software. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Unit Testing in the OO Context With OO the concept of the unit changes. Because of the dependence of sub classes, unit testing is a bit more complicated. In the OO context, unit testing is basically Class testing. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Integration Testing in the OO Context Unlike non OO programming, OO programming does not have an hierarchical control structure. Integrating one object at a time is also difficult because of the direct and indirect interactions of the components that make up the class. There are two basic strategies: Thread-based Use-based Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Thread-based testing integrates the set of classes required to respond to one input or event for the system. Each thread is integrated and tested individually. Regression testing is applied to ensure no side effects occur. Use-based testing begins the construction of system by testing those classes that use very few server classes. After independent classes are tested, the next layer of classes, called dependent classes are tested. This continues until the entire system is constructed. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Drivers can be used to test operations at the lowest level and for testing groups of classes. A driver may be used to replace the user interface. Stubs may be used where collaboration between classes is required but one or more of the collaborating classes is not fully implemented. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Cluster testing is one step in integration testing of OO software. Here, a cluster of collaborating classes is exercised by designing test cases that attempt to uncover errors in the collaborations. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Validation Testing Validation testing begins at the culmination of integrations testing. Testing focuses on the user-visible actions and user-recognizable output from the system. Validation can be defined as: Validation succeeds when software functions in a manner that can be reasonably expected by the customer. Software validation is achieved through a series of tests that demonstrate conformity with software requirements. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Most software product builders use a process called alpha and beta testing to uncover errors that only the end-user seems able to find. The alpha test is conducted at the developer’s site by end-users. The beta test is conducted at the end-user sites. Beta tests usually do not have the developer present. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE System Testing Recovery Testing – most computer-based systems must recover from faults and resume processing within a prespecified time. Recovery testing is a system test that forces the software to fail in a variety of ways and verifies that recovery is properly preformed. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Security Testing – Any computer system that manages sensitive information or causes actions that can improperly harm or benefit individuals is a target for improper or illegal penetration. Lot’s of security issues. Security testing verifies that protection mechanisms built into the system will, in fact, protect it from improper penetration. During security testing, the tester plays the role(s) of individual who desires to penetrate the system. Anything goes! What is the biggest source of security issues? Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Usually it’s not the software, but people issues. People often give out secure information. No system can truly protect against this 100%. Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Stress Testing So far all testing assumed normal program functions and performance. Stress tests are designed to confront programs with abnormal quantity, frequency, or volume. Multiple interrupts per second Increased data rate Test max memory Excessive disk hunting Software Engineering – Software Testing Strategies TEST STRATEGIES FOR OBJECT-ORIENTED SOFTWARE Performance Testing Designed to test the run-time performance of software within the context of an integrated system. Should be performed at all steps of the testing process. Not until system elements are fully integrated that performance of a system can really be ascertained. Sometime coupled with stress testing. Often requires hardware and software instrumentation to measure resource utilization.
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