Software testing and analysis

SOFTWARE TESTING AND ANALYSIS BY 360LOGICA

ULTIMATE GOAL FOR SOFTWARE TESTING Quality Assurance A L E A D I N G S O F T WA R E T E S T I N G - 360LOGICA

V & V GOALS Verification and validation should establish confidence that the software is fit for purpose This does NOT mean completely free of defects Rather, it must be good enough for its intended use and the type of use will determine the degree of confidence that is needed A LEADING SOFTWARE TESTING - 360LOGICA

VERIFICATION VS. VALIDATION • Verification: The software should conform to its specification (Are we building the product right?) • Validation: The software should do what the user really requires (Are we building the right product?) A LEADING SOFTWARE TESTING - 360LOGICA

“CLASSICAL” LIFECYCLE MODEL Requirements Phase Specification Phase (Analysis) Planning Phase Design Phase Implementation Phase Integration and Testing Maintenance Retirement A LEADING SOFTWARE TESTING - 360LOGICA

COST TO FIX FAULTS 60* to 100* 1.5* to 6* Cost 1* Definition Development Post Release A LEADING SOFTWARE TESTING - 360LOGICA

THE V & V PROCESS • Is a whole life-cycle process - V & V must be applied at each stage in the software process. • Has two principal objectives – The discovery of defects in a system – The assessment of whether or not the system is usable in an operational situation. A LEADING SOFTWARE TESTING - 360LOGICA

STATIC AND DYNAMIC VERIFICATION • Software inspections and walkthroughs - Concerned with analysis of the static system representation to discover problems (static verification) • Software testing - Concerned with exercising and observing product behaviour (dynamic verification) – The system is executed with test data and its operational behaviour is observed A LEADING SOFTWARE TESTING - 360LOGICA

STATIC AND DYNAMIC V&V Static verification Requirements High-level Formal Detailed specification Program specification design design Dynamic Prototype validation A LEADING SOFTWARE TESTING - 360LOGICA

V & V PLANNING • Careful planning is required to get the most out of testing and inspection processes • Planning should start early in the development process • The plan should identify the balance between static verification and testing • Test planning is about defining standards for the testing process rather than describing product tests A LEADING SOFTWARE TESTING - 360LOGICA

THE V-MODEL OF DEVELOPMENT Requir ements System System Detailed specification specification design design System Sub-system Module and Acceptance integration integration unit code test plan test plan test plan and tess Acceptance System Sub-system Service test integration test integration test A LEADING SOFTWARE TESTING - 360LOGICA

THE STRUCTURE OF A SOFTWARE TEST PLAN The testing process Requirements traceability Tested items Testing schedule Test recording procedures Hardware and software requirements Constraints A LEADING SOFTWARE TESTING - 360LOGICA

WALKTHROUGHS Informal examination of a product (document) Made up of:  developers  client  next phase developers  Software Quality Assurance group leader Produces:  list of items not understood  list of items thought to be incorrect F T W A R E T E S T I N G - 3 6 0 L O G I C A A LEADING SO

SOFTWARE INSPECTIONS Involve people examining the source representation with the aim of discovering anomalies and defects Do not require execution of a system so may be used before implementation May be applied to any representation of the system (requirements, design, test data, etc.) Very effective technique for discovering errors A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTION SUCCESS Many different defects may be discovered in a single inspection. In testing, one defect may mask another so several executions are required The reuse domain and programming knowledge so reviewers are likely to have seen the types of error that commonly arise A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTIONS AND TESTING Inspections and testing are complementary and not opposing verification techniques Both should be used during the V & V process Inspections can check conformance with a specification but not conformance with the customer‟s real requirements Inspections cannot check non-functional characteristics such as performance, usability, etc. A LEADING SOFTWARE TESTING - 360LOGICA

PROGRAM INSPECTIONS Formalised approach to document reviews Intended explicitly for defect DETECTION (not correction) Defects may be logical errors, anomalies in the code that might indicate an erroneous condition (e.g. an un-initialised variable) or non-compliance with standards A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTION PRE-CONDITIONS A precise specification must be available Team members must be familiar with the organisation standards Syntactically correct code must be available An error checklist should be prepared Management must accept that inspection will increase costs early in the software process Management must not use inspections for A LEADING SOFTWARE TESTING - 360LOGICA staff

INSPECTION PROCEDURE System overview presented to inspection team Code and associated documents are distributed to inspection team in advance Inspection takes place and discovered errors are noted Modifications are made to repair discovered errors Re-inspection may or may not be required A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTION TEAMS Made up of at least 4 members Author of the code being inspected Inspector who finds errors, omissions and inconsistencies Reader who reads the code to the team Moderator who chairs the meeting and notes discovered errors Other roles are Scribe and Chief moderator A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTION CHECKLISTS Checklist of common errors should be used to drive the inspection Error checklist is programming language dependent The 'weaker' the type checking, the larger the checklist Examples: Initialization, Constant naming, loop termination, array bounds, etc. A LEADING SOFTWARE TESTING - 360LOGICA

INSPECTION RATE 500 statements/hour during overview 125 source statement/hour during individual preparation 90-125 statements/hour can be inspected Inspection is therefore an expensive process Inspecting 500 lines costs about 40 man/hours effort (@ $50/hr = $2000!!!) A LEADING SOFTWARE TESTING - 360LOGICA

PROGRAM TESTING • Can reveal the presence of errors NOT their absence • A successful test is a test which discovers one or more errors • The only validation technique for non- functional requirements • Should be used in conjunction with static verification to provide full V&V coverage A LEADING SOFTWARE TESTING - 360LOGICA

EXECUTION BASED TESTING “Program testing can be a very effective way to show the presents of bugs but is hopelessly inadequate for showing their absence” [Dijkstra] Fault: “bug” incorrect piece of code Failure: result of a fault Error: mistake made by the programmer/developer A LEADING SOFTWARE TESTING - 360LOGICA

TESTING AND DEBUGGING • Defect testing and debugging are distinct processes • Verification and validation is concerned with establishing the existence of defects in a program • Debugging is concerned with locating and repairing these errors • Debugging involves formulating a hypothesis about program behaviour then testing these hypotheses to find the system error A LEADING SOFTWARE TESTING - 360LOGICA

THE DEBUGGING PROCESS Test Test results Specification cases Locate Design Repair Re-test error error repair error program A LEADING SOFTWARE TESTING - 360LOGICA

TESTING PHASES Component Integration testing testing Software developer Independent testing team A LEADING SOFTWARE TESTING - 360LOGICA

TESTING PHASES Component testing  Testing of individual program components  Usually the responsibility of the component developer (except sometimes for critical systems)  Tests are derived from the developer’s experience Integration testing  Testing of groups of components integrated to create a system or sub-system  The responsibility of an independent testing team  Tests are based onA aEsystemT W A R E T E S T I N G - 3 6 0 L O G I C A L A D I N G S O F specification

TESTING PRIORITIES • Only exhaustive testing can show a program is free from defects. However, exhaustive testing is impossible • Tests should exercise a system's capabilities rather than its components • Testing old capabilities is more important than testing new capabilities • Testing typical situations is more important than boundary value cases A LEADING SOFTWARE TESTING - 360LOGICA

TEST DATA AND TEST CASES • Test data Inputs which have been devised to test the system • Test cases Inputs to test the system and the predicted outputs from these inputs if the system operates according to its specification A LEADING SOFTWARE TESTING - 360LOGICA

DEVELOPMENT OF TEST CASES Test cases and test scenarios comprise much of a software systems testware. Black box test cases are developed by domain analysis and examination of the system requirements and specification. Glass box test cases are developed by examining the behavior of the source code. A LEADING SOFTWARE TESTING - 360LOGICA

THE DEFECT TESTING PROCESS Test Test Test Test cases data results reports Design test Prepare test Run program Compare results cases data with test data to test cases A LEADING SOFTWARE TESTING - 360LOGICA

METHODS OF TESTING Test to specification:  Black box,  Data driven  Functional testing  Code is ignored: only use specification document to develop test cases Test to code:  Glass box/White box  Logic driven testing  Ignore specification and only examine the code. A LEADING SOFTWARE TESTING - 360LOGICA

CAN YOU GUARANTEE A PROGRAM IS CORRECT? This is called the Halting Problem Write a program to test if any given program is correct. The output is correct or incorrect. Test this program on itself. If output is incorrect, then how do you know the output is correct? Conundrum, Dilemma, or Contradiction? A LEADING SOFTWARE TESTING - 360LOGICA

BLACK-BOX TESTING An approach to testing where the program is considered as a „black-box‟ The program test cases are based on the system specification Test planning can begin early in the software process A LEADING SOFTWARE TESTING - 360LOGICA

BLACK-BOX TESTING I n p u t s c a u s i n g a n o m a l o u s Input test data I b e h a v i o u r e S y s t e m O u t p u t s w h i c h r e v e a l t h e p r e s e n c e o f Output test results Oe d e f e c t s A LEADING SOFTWARE TESTING - 360LOGICA

PAIRING DOWN TEST CASES Use methods that take advantage of symmetries, data equivalencies, and independencies to reduce the number of necessary test cases.  Equivalence Testing  Boundary Value Analysis Determine the ranges of working system Develop equivalence classes of test cases Examine the boundaries of these classes carefully A LEADING SOFTWARE TESTING - 360LOGICA

EQUIVALENCE PARTITIONING Input data and output results often fall into different classes where all members of a class are related Each of these classes is an equivalence partition where the program behaves in an equivalent way for each class member Test cases should be chosen from each partition A LEADING SOFTWARE TESTING - 360LOGICA

EQUIVALENCE PARTITIONING Invalid inputs Valid inputs System Outputs A LEADING SOFTWARE TESTING - 360LOGICA

BOUNDARY VALUE TESTING • Partition system inputs and outputs into „equivalence sets‟ – If input is a 5-digit integer between 10,000 and 99,999, equivalence partitions are < 10,000, 10,000 - 99, 999 and > 10, 000 • Choose test cases at the boundary of these sets – 00000, 09999, 10000, 99999, 10001 A LEADING SOFTWARE TESTING - 360LOGICA

EQUIVALENCE PARTITIONS 3 11 4 7 10 Less than 4 Between 4 and 10 More than 10 Number of input values 9999 100000 10000 50000 99999 Less than 10000 Between 10000 and 99999 More than 99999 Input values A LEADING SOFTWARE TESTING - 360LOGICA

SEARCH ROUTINE SPECIFICATION procedure Search (Key : ELEM ; T: ELEM_ARRAY; Found : in out BOOLEAN; L: in out ELEM_INDEX) ; Pre-condition -- the array has at least one element T’FIRST <= T’LAST Post-condition -- the element is found and is referenced by L ( Found and T (L) = Key) or -- the element is not in the array ( not Found and not (exists i, T’FIRSTI N>=O iF T<=R T’LAST,3 6 0 L (i)I C= Key )) A LEAD G S WA E TESTING - T OG A

SEARCH ROUTINE - INPUT PARTITIONS • Inputs which conform to the pre-conditions • Inputs where a pre-condition does not hold • Inputs where the key element is a member of the array • Inputs where the key element is not a member of the array A LEADING SOFTWARE TESTING - 360LOGICA

TESTING GUIDELINES - SEQUENCES Test software with sequences which have only a single value Use sequences of different sizes in different tests Derive tests so that the first, middle and last elements of the sequence are accessed Test with sequences of zero length A LEADING SOFTWARE TESTING - 360LOGICA

SEARCH ROUTINE - INPUT PARTITIONS Array Element Single value In sequence Single value Not in sequence More than 1 value First element in sequence More than 1 value Last element in sequence More than 1 value Middle element in sequence More than 1 value Not in sequence Input sequence (T) Key (Key) Output (Found, L) 17 17 true, 1 17 0 false, ?? 17, 29, 21, 23 17 true, 1 41, 18, 9, 31, 30, 16, 45 45 true, 7 17, 18, 21, 23, 29, 41, 38 23 true, 4 21, 23, 29, 33, 38 25 false, ?? A LEADING SOFTWARE TESTING - 360LOGICA

SORTING EXAMPLE Example: sort (lst, n)  Sort a list of numbers  The list is between 2 and 1000 elements Domains:  The list has some item type (of little concern)  n is an integer value (sub-range) Equivalence classes;  n<2  n > 1000  2 <= n <= 1000 A LEADING SOFTWARE TESTING - 360LOGICA

SORTING EXAMPLE What do you test? Not all cases of integers Not all cases of positive integers Not all cases between 1 and 1001 Highest payoff for detecting faults is to test around the boundaries of equivalence classes. Test n=1, n=2, n=1000, n=1001, and say n= 10 Five tests versus 1000. A LEADING SOFTWARE TESTING - 360LOGICA

WHITE-BOX TESTING • Sometime called structural testing or glass- box testing • Derivation of test cases according to program structure • Knowledge of the program is used to identify additional test cases • Objective is to exercise all program statements (not all path combinations) A LEADING SOFTWARE TESTING - 360LOGICA

TYPES OF STRUCTURAL TESTING Statement coverage -  Test cases which will execute every statement at least once.  Tools exist for help  No guarantee that all branches are properly tested. Loop exit? Branch coverage  All branches are tested once Path coverage - Restriction of type of paths:  Linear code sequences  Definition/Use checking (all definition/use paths)  Can locate dead code A LEADING SOFTWARE TESTING - 360LOGICA

WHITE-BOX TESTING Test data Tests Derives Component Test code outputs A LEADING SOFTWARE TESTING - 360LOGICA

WHITE BOX TESTING - BINARY SEARCH int EXAMPLE search ( int key, int [] elemArray) { int bottom = 0; int top = elemArray.length - 1; int mid; int result = -1; while ( bottom <= top ) { mid = (top + bottom) / 2; if (elemArray [mid] == key) { result = mid; return result; } // if part else { if (elemArray [mid] < key) bottom = mid + 1; else top = mid - 1; } } //while loop return result; } // search A LEADING SOFTWARE TESTING - 360LOGICA

BINARY SEARCH EQUIVALENCE PARTITIONS • Pre-conditions satisfied, key element in array • Pre-conditions satisfied, key element not in array • Pre-conditions unsatisfied, key element in array • Pre-conditions unsatisfied, key element not in array • Input array has a single value • Input array has an even number of values A LEADING SOFTWARE TESTING - 360LOGICA • Input array has an odd number of values

BINARY SEARCH EQUIVALENCE PARTITIONS Equivalence class boundaries Elements < Mid Elements > Mid Mid-point A LEADING SOFTWARE TESTING - 360LOGICA

BINARY SEARCH - TEST CASES Input array (T) Key (Key) Output ( Found, L ) 17 17 true, 1 17 0 false, ?? 17, 21, 23, 29 17 true, 1 9, 16, 18, 30, 31, 41, 45 45 true, 7 17, 18, 21, 23, 29, 38, 41 23 true, 4 17, 18, 21, 23, 29, 33, 38 21 true, 3 12, 18, 21, 23, 32 23 true, 4 21, 23, 29, 33, 38 25 false, ?? A LEADING SOFTWARE TESTING - 360LOGICA

PATH TESTING The objective of path testing is to ensure that the set of test cases is such that each path through the program is executed at least once The starting point for path testing is a program flow graph that shows nodes representing program decisions and arcs representing the flow of control Statements with conditions are therefore nodes in the flow graph A LEADING SOFTWARE TESTING - 360LOGICA

PROGRAM FLOW GRAPHS • Describes the program control flow. Each branch is shown as a separate path and loops are shown by arrows looping back to the loop condition node • Used as a basis for computing the cyclomatic complexity • Cyclomatic complexity = Number of edges - Number of nodes +2 A LEADING SOFTWARE TESTING - 360LOGICA

CYCLOMATIC COMPLEXITY • The number of tests to test all control statements equals the cyclomatic complexity • Cyclomatic complexity equals number of conditions in a program • Useful if used with care. Does not imply adequacy of testing • Although all paths are executed, all combinations of paths are not executed A LEADING SOFTWARE TESTING - 360LOGICA

BINARY SEARCH FLOW 1 GRAPH while bottom <= top bottom > top 2 3 if (elemArray [mid] == key 8 4 (if (elemArray [mid]< key 5 6 9 7 A LEADING SOFTWARE TESTING - 360LOGICA

INDEPENDENT PATHS • 1, 2, 3, 8, 9 • 1, 2, 3, 4, 6, 7, 2 • 1, 2, 3, 4, 5, 7, 2 • 1, 2, 3, 4, 6, 7, 2, 8, 9 • Test cases should be derived so that all of these paths are executed • A dynamic program analyser may be used to check that paths have been executed A LEADING SOFTWARE TESTING - 360LOGICA

FEASIBILITY Pure black box testing (specification) is realistically impossible because there are (in general) too many test cases to consider. Pure testing to code requires a test of every possible path in a flow chart. This is also (in general) infeasible. Also every path does not guarantee correctness. Normally, a combination of Black box and Glass box testing is done. A LEADING SOFTWARE TESTING - 360LOGICA

INTEGRATION TESTING Tests complete systems or subsystems composed of integrated components Integration testing should be black-box testing with tests derived from the specification Main difficulty is localising errors Incremental integration testing reduces this problem A LEADING SOFTWARE TESTING - 360LOGICA

INCREMENTAL INTEGRATION TESTING A T1 T1 A T1 T2 A B T2 T2 B T3 T3 B C T3 T4 C T4 D T5 Test sequence Test sequence Test sequence 1 2A L E A D I N G SOFTWARE 3 TESTING - 360LOGICA

APPROACHES TO INTEGRATION TESTING Top-down testing  Start with high-level system and integrate from the top-down replacing individual components by stubs where appropriate Bottom-up testing  Integrate individual components in levels until the complete system is created In practice, most integration involves a combination of these strategies A LEADING SOFTWARE TESTING - 360LOGICA

TOP-DOWN TESTING Testing Level 1 Level 1 . .. sequence Level 2 Level 2 Le vel 2 Level 2 Le vel 2 stubs Le vel 3 stubs A LEADING SOFTWARE TESTING - 360LOGICA

BOTTOM-UP TESTING Test drivers Testing Level N Level N Le vel N Level N Level N sequence Test drivers Level N–1 Level N–1 Level N–1 A LEADING SOFTWARE TESTING - 360LOGICA

SOFTWARE TESTING METRICS Defects rates Errors rates Number of errors Number of errors found per person hours expended Measured by:  individual  module  during development Errors should be categorized by origin, type, cost A LEADING SOFTWARE TESTING - 360LOGICA

MORE METRICS Direct measures - cost, effort, LOC, etc. Indirect Measures - functionality, quality, complexity, reliability, maintainability Size Oriented:  Lines of code - LOC  Effort - person months  errors/KLOC  defects/KLOC  cost/KLOC A LEADING SOFTWARE TESTING - 360LOGICA

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