1 CHAPTER 17 SOFTWARE TESTING STRATEGIES. December 28, 1997 R. A. Volz -- Assistance - Nirmal Patil 2 TOPICS u A strategic approach to software testing

1

CHAPTER 17CHAPTER 17

SOFTWARE TESTING SOFTWARE TESTING STRATEGIESSTRATEGIES

December 28, 1997 R. A. Volz -- Assistance - Nirmal Patil2

TOPICSTOPICS

A strategic approach to software testing Unit Testing Integration Testing Validation Testing System Testing The ART of Debugging Summary


STRATEGIC APPROACH TO STRATEGIC APPROACH TO SOFTWARE TESTING SOFTWARE TESTING

Generic characteristics of software testing strategies:-

Testing begins at module level and works outward towards the of integration entire computer based system.

Different testing techniques are required at different points in time.

Testing is conducted by the s/w developer and ITG ( Independent Test Group ) for large projects.

Testing and Debugging are different and Debugging is essential in any testing strategy.


Verification and ValidationVerification and Validation

Verification -- Does the product meet its specifications?

Validation -- Does the product perform as desired?


Software Testing StrategySoftware Testing Strategy

A Software Testing Strategy


Software Testing StrategySoftware Testing Strategy


Software Error ModelSoftware Error Model

f(t) = cumulative remaining errors at time t l0 = initial failure rate p = exponential reduction as errors repaired

f(t) = (1/p)ln(l0pt + 1)


STRATEGIC APPROACHSTRATEGIC APPROACH

Issues to be addressed to develop a successful software testing strategy: Specify product requirements in a quantifiable

manner long before testing commences. State testing objectives explicitly. Understand the users of the software. Develop testing plan that emphasizes “rapid

cycle testing.”


STRATEGIC APPROACHSTRATEGIC APPROACH

Issues to be addressed to develop a successful software testing strategy:

Build robust software that is designed to test itself.

Use effective formal technical reviews as a filter to testing.

Conduct formal technical reviews to assess test strategy and test cases.

Develop continuous improvement approach


UNIT TESTINGUNIT TESTING

Unit testing -- focuses on the smallest element of software design viz. the module. Corresponds to class testing in the OO context.

Makes heavy use of white-box testing.


UNIT TESTINGUNIT TESTING

Unit Test Generation Considerations:

Review Design information - develop unit test cases.

Test

cases

interfacelocal data structuresboundary conditionsindependent pathserror handling paths

driver

Module to be tested

stubstub


Unit Test GenerationUnit Test Generation

Interface considerations # of input parameters = # arguments? Parameter and argument attributes match? Parameter and argument units match? Order correct (if important)? Number and order of arguments for built-ins? References to parms not associated with entry point? Attempt to modify input-only arguments? Global variable definitions consistent? Constraints passed as arguments?



External I/O considerations Files attributes correct? OPEN/CLOSE correct?

Format specification matches I/O statement? Buffer size matches record size? Files opened before use? EOF handled correctly?

I/O errors handled? Textual errors in output?



Data structure considerations Improper or inconsistent typing? Erroneous initialization or default values? Incorrect variable names? Inconsistent data types? Underflow, overflow and addressing

exceptions?


Unit Test GenerationUnit Test Generation Test cases must cover all execution paths Common computational errors to be checked:

incorrect arithmetic mixed mode operations incorrect initialization precision inaccuracy incorrect symbolic representation of expression

Other tests needed incompatible data types in comparisons incorrect logical operators or precedence comparison problems (e.g., == on floats) loop problems



Error handling tests Exception-handling is incorrect? Error description is unintelligible, insufficient or

incorrect? Error condition causes system interrupt before

error handling completed?


INTEGRATION TESTINGINTEGRATION TESTING

A systematic approach for constructing program structure while conducting tests to uncover errors associated with interfacing.

Tendency for Non-Incremental integration.. Big Bang approach …. Chaos !! ( usually ).

Incremental integration - program is constructed and tested in small segments. Top-Down Integration testing Bottom-Up Integration testing





Top-Down Approach Begin construction and testing with main module.

Stubs are substituted for all subordinate modules. Subordinate stubs are replaced one at a time by

actual modules. Tests are conducted as each module is integrated. On completion of each set of tests, another stub is

replaced with the real module. Regression testing may be conducted to ensure

that new errors have not been introduced.


Top Down Approach - Use StubsTop Down Approach - Use Stubs


INTEGRATION TESTING INTEGRATION TESTING

Top-Down Approach : Advantages:

Verifies major control or decision points early in the test process.

With the use of depth-first integration testing, a complete function of the software can be demonstrated. -- Confidence builder for developer/customer.

Disadvantages: Since stubs replace lower level modules, no

significant data can flow upwards to the main module.



Bottom Up Approach : This approach begins construction and testing

with modules at the lowest levels in the program structure.

Low-level modules are combined into clusters. A driver is written to coordinate test case input and

output. The cluster is tested. Drivers are removed and clusters are combined

moving upward in the program hierarchy.


Bottom Up ApproachBottom Up Approach



Bottom Up Approach Advantages:

Easier test case design and lack of stubs.

Disadvantages: The program as an entity is does not exist until the

last module is added.

Sandwich Testing:- combined approach Top down strategy for upper levels and Bottom

up strategy for subordinate levels.


INTEGRATION TESTINGINTEGRATION TESTING Regression Testing

Re-execution of some subset of tests already conducted to ensure that the new changes do not have unintended side effects.

The Regression test suite should contain three different classes of test cases : A representative sample of tests that will

exercise all software functions Additional tests that focus on functions that are

likely to be affected by the change. Tests that focus on software components that

have changed.


INTEGRATION TESTINGINTEGRATION TESTINGIntegration Test Documentation

Order ofIntegration

Scope of testing

1 2 3 4

Test planTest

Procedure nActual Test

Results

5

Ref. &Appendix

Test phases and builds

Schedule

Overheadsoftware

Environment / Resources

Unit test

Test environment

Test case data

Expected Results

for build n


VALIDATION TESTINGVALIDATION TESTING

It provides final assurance that software meets all functional, behavioral, and performance requirements.-- Exclusive use of Black-box testing techniques.

After each validation test case either software conforms to specs or a deviation from specs is detected and a deficiency list needs to be worked.

Alpha and Beta testing Alpha test -- At developer’s site by customer. Beta test -- At customer’s site in a “live”

environment.


SYSTEM TESTINGSYSTEM TESTING

A series of tests to verify that all system elements have been properly integrated.

Recovery Testing: Forces software to fail in a variety of ways and verifies

that recovery is properly performed. Security Testing:

Attempts to verify the software’s protection mechanisms. The software designer tries to make penetration cost more than the value of information obtained by breaking in.


SYSTEM TESTING SYSTEM TESTING

Stress Testing: Executes the system in a manner that demands

resources in abnormal quantity, frequency or volume.

Performance Testing: To test the run time performance of a system

within the context of an integrated system.

CLCS Test ApproachCLCS Test Approach

Developers

System Integration and Test Group

Validation Group

Application S/W IPT

Users

Operations Environment User Acceptance Tests

Development Environment

UnitTestDesign

Early User Eval

Unit IntegTest

Integration Environment

System TestCOTS H/Won Dock

User Eval CSCI IntTest

System Delivery

AcceptanceTest

System S/W Validation Tests

User App S/W Validation Tests


THE ART OF DEBUGGINGTHE ART OF DEBUGGING

Debugging is a consequence of successful testing -- when a test case uncovers an error, it is the debugging process that results in the removal of the error.

Debugging is an ART. The external manifestation of the error and the cause of the error normally do not share an obvious relationships.



The Debugging process

Test cases

Execution of test cases Results

Debugging

Suspected causes

Additional tests

Identified causesCorrections

Regression tests



Debugging Approaches Brute force : - Take memory dumps, invoke run

time traces. Least efficient and quite common. Backtracking :- Once an error is uncovered, trace

your way back to the cause of the error.

Cause Elimination : - Isolate potential causes,

devise cause hypotheses tests to isolate bug. Use of debugging tools


COMMENTSCOMMENTS

Should the software developer be involved with testing ? Developer’s have a vested interest in

demonstrating that their software is error-free. Developer’s (psychologically) feel that testing

is destructive. When are we done with testing ?

“You are never done with testing, the burden shifts from you to the customer.”


SUMMARYSUMMARY

Software Testing accounts for the largest percentage of technical effort in the software process.

Objective of Software testing -- To uncover errors, maintain software quality.

Steps : Unit, Integration, Validation, System. Debugging is often an art and the most

valuable resource is often the counsel of other software engineers.

Documents

1 CHAPTER 17 SOFTWARE TESTING STRATEGIES. December 28, 1997 R. A. Volz -- Assistance - Nirmal Patil 2 TOPICS u A strategic approach to software testing