CS 451 Software Engineering Winter 2009

Transcription

1 CS 451 Software Engineering Winter 2009 Yuanfang Cai Room 104, University Crossings

2 Testing Process

3 Testing Testing only reveals the presence of defects Does not identify nature and location of defects Identifying & removing the defect => role of debugging and rework Preparing test cases, performing testing, defects identification & removal all consume effort Overall testing becomes very expensive : 30-50% development cost

4 Levels of Testing The code contains requirement defects, design defects, and coding defects Nature of defects is different for different injection stages One type of testing will be unable to detect the different types of defects Different levels of testing are used to uncover these defects

5 Levels of Testing User needs Acceptance testing Requirement specification System testing Design Integration testing code Unit testing

6 Unit Testing Different modules tested separately Focus: defects injected during coding Essentially a code verification technique, covered in previous chapter UT is closely associated with coding Frequently the programmer does UT; coding phase sometimes called coding and unit testing

7 Integration Testing Focuses on interaction of modules in a subsystem Unit tested modules combined to form subsystems Test cases to exercise the interaction of modules in different ways May be skipped if the system is not too large

8 System Testing Entire software system is tested Focus: does the software implement the requirements? Validation exercise for the system with respect to the requirements Generally the final testing stage before the software is delivered May be done by independent people Defects removed by developers Most time consuming test phase

9 Acceptance Testing Focus: Does the software satisfy user needs? Generally done by end users/customer in customer environment, with real data Only after successful AT software is deployed Any defects found,are removed by developers Acceptance test plan is based on the acceptance test criteria in the SRS

10 Other forms of testing Performance testing tools needed to measure performance Stress testing load the system to peak, load generation tools needed Regression testing test that previous functionality works alright important when changes are made Previous test records are needed for comparisons Prioritization of testcases needed when complete test suite cannot be executed for a change Smoke testing Nightly build

11 Defect logging and tracking A large software may have thousands of defects, found by many different people Often person who fixes (usually the coder) is different from who finds Due to large scope, reporting and fixing of defects cannot be done informally Defects found are usually logged in a defect tracking system and then tracked to closure Defect logging and tracking is one of the best practices in industry

12 Defect logging A defect in a software project has a life cycle of its own, like Found by someone, sometime and logged along with info about it (submitted) Job of fixing is assigned; person debugs and then fixes (fixed) The manager or the submitter verifies that the defect is indeed fixed (closed) More elaborate life cycles possible

13 Validation and Verification Validation: a different set of activities that ensures that the software that has been built is traceable to customer requirements. Are we building the right product? Verification: the set of activities the ensures that software correctly implements a specific function. Are we building the product right?

14 Organizing Testing Software testing may be viewed as a spiral process: 15

15 Organizing Testing Software Testing Steps 16

16 Software Testing Strategies 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. 17

17 Strategic Issues 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. 18

18 Unit Testing

19 Testing 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. 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. 20

20 Testing Strategies Unit Testing Procedure Unit testing is normally considered as an adjunct to the coding step. Design of tests can be done before coding begins (Agile programming) 21

21 Testing Strategies Unit Testing Procedure 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 to 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. Unit testing is simpler when modules are highly cohesive. 22

22 Junit Example Java Code to Test public class Math { static public int add(int a, int b) { return a + b; } }

23 Junit example JUNIT test case import junit.framework.*; public class TestMath extends TestCase { public void testadd() { int num1 = 3; int num2 = 2; int total = 5; int sum = 0; sum = Math.add(num1, num2); assertequals(sum, total); } }

24 Integration Testing

25 Integration 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. 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.

26 Integration Testing There is a tendency to attempt non-incremental integration construct the whole program via a bigbang approach. Thus to combine all components at once and test it as an entire program. 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.

27 Integration Testing -- Top Down Modules subordinate to the main control module are incorporated into the structure in either a depth first or breath first manner.

28 Integration Testing -- Top Down 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.

29 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.

30 Bottom Up Integration

31 Regression Testing

32 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.

33 Testing in the OO Context

34 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. Cannot simply test methods in a super class and assume they are still valid in each subclass Subclasses may re-define important attributes or subordinate methods Must fully test all methods of all classes

35 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

36 Test Strategies for OO 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. Good for GUIs, other event-driven multithreaded software

37 Test Strategies for OO Software 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. AKA: Bottom-up testing with objects

38 Test Strategies for OO 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.

39 Test Strategies for OO 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.

40 Validation Testing 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.

41 Test Strategies for Publicly-used Software What to do if your product does not have one or a few customers? 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.

42 Recovery 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.

43 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. In your code In libraries and frameworks In database access In OS layers Security testing finds faults with the protection mechanisms built into the system that may allow improper access.

44 Security Testing During security testing, the tester plays the role(s) of individual who desires to penetrate the system. Penetration testing requires high skill and the ability to think outside the box Best to get an independent testing group that specializes in penetration testing Usually it s not the software, but people issues. People often give out secure information. No system can truly protect against this 100%.

45 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

46 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. Often requires hardware and software instrumentation to measure resource utilization.

47 Summary Validation and Verification Different Types of Testing Context purposes