jpf@fe.up.pt www.fe.up.pt/~jpf TQS - Teste e Qualidade de Software (Software Testing and Quality) Introduction To Software Testing Concepts João Pascoal Faria jpf@fe.up.pt www.fe.up.pt/~jpf

Software testing Software testing consists of the dynamic (1) verification of the behavior of a program on a finite (2) set of test cases, suitably selected (3) from the usually infinite executions domain, against the specified expected (4) behavior [source: SWEBOK] (1) testing always implies executing the program on some inputs (2) for even simple programs, too many test cases are theoretically possible that exhaustive testing is infeasible trade-off between limited resources and schedules and inherently unlimited test requirements (3) see test case design techniques later on how to select the test cases (4) it must be possible to decide whether the observed outcomes of the program are acceptable or not the pass/fail decision is commonly referred to as the oracle problem

Purpose of software testing The main purpose of software testing is to find defects "The goal of a software tester is to find bugs, find them as early as possible, and make sure that they get fixed" (source: Ron Patton) The best test cases are the ones with higher probability of revealing defects / bugs Testing does not prove the absence of defects!

Test cases Test case - Inputs to test the system and the expected outputs from these inputs if the system operates correctly Inputs may include an initial state of the system Outputs may include a final state of the system When test cases are executed, the system is provided with the specified inputs and the actual outputs are compared with the outputs expected Example for a calculator: 3 + 5 (input) should give 8 (output)

Types of testing Level of detail or phase Accessibility system integration unit Accessibility (test case design strategy/technique) security robustness white box black box performance usability reliability functional behaviour focus here Characteristics

Test levels or phases (1) Unit testing Testing of individual program units or components Usually the responsibility of the component developer (except sometimes for critical systems) Tests are based on experience, specifications and code A principal goal is to detect functional and structural defects in the unit Integration testing Testing of groups of components integrated to create a sub-system Usually the responsibility of an independent testing team (except sometimes in small projects) Tests are based on a system specification (technical specifications, designs) A principal goal is to detect defects that occur on the interfaces of units and their common behavior

Test levels or phases (2) System testing Testing the system as a whole Usually the responsibility of an independent testing team Tests are usually based on a requirements document (functional requirements/specifications and quality requirements) A principal goal is to evaluate attributes such as usability, reliability and performance (assuming unit and integration testing have been performed) Acceptance testing Usually the responsibility of the customer Tests are based on a requirements specification or a user manual A principal goal is to check if the product meets customer requirements and expectations (source: I. Sommerville)

Test levels and the extended V-model of software development Execute acceptance tests Specify Requirements Execute system tests System/acceptance test plan & test cases review/audit Requirements review Specify/Design Code System/acceptance tests Design Execute integration tests Integration test plan & test cases review/audit Design review Specify/Design Code Integration tests Code Execute unit tests Unit test plan & test cases review/audit Code reviews (source: I. Burnstein, pg.15) Specify/Design Code Unit tests

Typical tests and reviews (source: "Software Project Survival Guide", Steve McConnell)

Test harness Auxiliary code developed to support testing Test drivers call the target code simulate calling units or a user where test procedures and test cases are coded (for automatic test case execution) or a user interface is created (for manual test case execution) Test stubs simulate called units simulate modules/units/systems called by the target code

Good practices Write the test cases before the software to be tested applies to any level: unit, integration or system helps getting insight into the requirements Code the test cases because of the frequent need for regression testing (repetition of testing each time the software is modified)

References and further reading Practical Software Testing, Ilene Burnstein, Springer-Verlag, 2003 Software Testing, Ron Patton, SAMS, 2001 Testing Computer Software,  2nd Edition, Cem Kaner, Jack Falk, Hung Nguyen, John Wiley & Sons, 1999 Software Engineering, Ian Sommerville, 6th Edition, Addison-Wesley, 2000 Guide to the Software Engineering Body of Knowledge (SWEBOK), IEEE Computer Society, http://www.swebok.org/