Testing
Lecture Software 28&29
Software Engineering, COMP201
Slide 1
Defect testing
q
Testing programs to establish the presence of system defects
Software Engineering, COMP201
Slide 2
Objectives
q
q q
q
To understand testing techniques that are geared to discover program faults To introduce guidelines for interface testing To understand specific approaches to objectoriented testing To understand the principles of CASE tool support for testing
Software Engineering, COMP201
Slide 3
Topics covered
q q q q
Defect testing Integration testing Object-oriented testing Testing workbenches
Software Engineering, COMP201
Slide 4
The testing process
q
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 Testing of groups of components integrated to create a system or sub-system The responsibility of an independent testing team Tests are based on a system specification
q
Integration testing
Software Engineering, COMP201
Slide 5
Testing phases
C p en om on t te g stin Softwa d re evelop er
In ration teg te g stin In end testin team dep ent g
Software Engineering, COMP201
Slide 6
Defect testing
q
q
q
The goal of defect testing is to discover defects in programs A successful defect test is a test which causes a program to behave in an anomalous way Tests show the presence not the absence of defects
Software Engineering, COMP201
Slide 7
Testing priorities
q
q
q
q
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
Software Engineering, COMP201 Slide 8
Test data and test cases
q
q
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
Software Engineering, COMP201
Slide 9
The defect testing process
Test cases
Test data
Test results
Test reports
Design test cases
Prepare test data
Run program with test data
Compare r esults to test cases
Software Engineering, COMP201
Slide 10
Black-box testing
q
q
q
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
Software Engineering, COMP201
Slide 11
Black-box testing
I p t te t d ta nu s a I
e
I p tsc u i g n u a sn a o ao s n ml u b h vo r eai u
Ss m y te
Otp tte t r s l u u s e uts
O e
Otp t wi hr v a u us hc e e l th p e e c o e r sn e f df c ee ts
Software Engineering, COMP201
Slide 12
Equivalence partitioning
q
q
q
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
Software Engineering, COMP201
Slide 13
Equivalence partitioning
In alid inp v uts
V inp alid uts
S tem ys
O u utp ts
Software Engineering, COMP201
Slide 14
Equivalence partitioning
q
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
q
Choose test cases at the boundary of these sets
00000, 09999, 10000, 99999, 10001
Software Engineering, COMP201
Slide 15
Equivalence partitions
3 4 7 1 1 1 0
Ls t a 4 es hn
Bt e n4 n 1 ewe a d 0
Methn1 o a 0 r
Nme o i p tv l e u br f n u au s 99 99 100 00 500 00 100 000 999 99
Ls t a 1 0 0 es hn 00 I p tvl e n u au s
Bt e n1 0 0 n 9 9 9 ewe 0 0 a d 9 9
M ethn9 9 9 o a 99 r
Software Engineering, COMP201
Slide 16
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'FIRST >= i <= T'LAST, T (i) = Key ))
Software Engineering, COMP201
Slide 17
Search routine - input partitions
q q q
q
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
Software Engineering, COMP201
Slide 18
Testing guidelines (sequences)
q
q
q
q
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
Software Engineering, COMP201
Slide 19
Search routine - input partitions
Software Engineering, COMP201
Slide 20
Structural testing
q q
q
Sometime called white-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)
Software Engineering, COMP201
Slide 21
White-box testing
T data est
T ests
D es eriv C p en om on t co de T est ou uts tp
Software Engineering, COMP201
Slide 22
class BinSearch { // // // // // // // This is an encapsulation of a binary search function that takes an array of ordered objects and a key and returns an object with 2 attributes namely index - the value of the array index found - a boolean indicating whether or not the key is in the array An object is returned because it is not possible in Java to reference to a function and so return two values the key is -1 if the element is not found
pass
basic
types
by
public static void search ( int key, int [] elemArray, Result r ) { int bottom = 0 ; int top = elemArray.length - 1 ; int mid ; r.found = false ; r.index = -1 ; while ( bottom <= top ) { mid = (top + bottom) / 2 ; if (elemArray [mid] == key) { r.index = mid ; r.found = true ; return ; } // if part else { if (elemArray [mid] < key) bottom = mid + 1 ; else top = mid - 1 ; } } //while loop } // search } //BinSearch
Binary search (Java)
Binary search - equiv. partitions
q q
q q q q q
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 Input array has an odd number of values
Software Engineering, COMP201
Slide 24
Binary search equiv. partitions
E i a n c s b n re q vec l s o di s u l e a ua
Em s M l et < i e n d
Em s M l et > i e n d
Mp n i - ot d i
Software Engineering, COMP201
Slide 25
Binary search - test cases
Software Engineering, COMP201
Slide 26
Path testing
q
q
q
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
Software Engineering, COMP201 Slide 27
Program flow graphs
q
q
q
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
Software Engineering, COMP201
Slide 28
Cyclomatic complexity
q
q
q
q
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
Software Engineering, COMP201
Slide 29
1
bottom > top
while bottom <= top 2
3
if (elemArray [mid] == key
8 5 9
4
(if (elemArray [mid]< key 6
7
Binary search flow graph
Independent paths
q q q q q
q
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
Software Engineering, COMP201
Slide 31
Integration testing
q
q
q q
Tests complete systems or subsystems composed of components integrated Integration testing should be black-box testing with tests derived from the specification Main difficulty is localising errors Incremental integration testing reduces this problem
Software Engineering, COMP201
Slide 32
Incremental integration testing
A A T1 A T2 B T3 C T4 D Test sequence 1 Test sequence 2
Software Engineering, COMP201
T1
T1 T2 T2 B T3 T3 C T4
B
T5 Test sequence 3
Slide 33
Approaches to integration testing
q
Top-down testing
Start with high-level system and integrate from the top-down replacing individual components by stubs where appropriate Integrate individual components in levels until the complete system is created
q
Bottom-up testing
q
In practice, most integration involves a combination of these strategies
Software Engineering, COMP201
Slide 34
1.
For which types of system is bottom-up testing appropriate, and why? Answer: Object-oriented systems because these have a neat decomposition into classes and methods makes testing easy real-time systems because we can identify slow bits of code more quickly systems with strict performance requirements because we can measure the performance of individual methods early in the testing process
Software Engineering, COMP201 Slide 35
q q
q q
q
q
Top-down testing
Level 1 Testing sequence Level 1 . ..
Level 2 Level 2 stubs
Level 2
Level 2
Level 2
Level 3 stubs
Software Engineering, COMP201
Slide 36
Bottom-up testing
Test drivers Level N Level N Level N Level N Level N Testing sequence
Test drivers
Level N1
Level N1
Level N1
Software Engineering, COMP201
Slide 37
Tetsing approaches
q
Architectural validation
Top-down integration testing is better at discovering errors in the system architecture Top-down integration testing allows a limited demonstration at an early stage in the development Often easier with bottom-up integration testing Problems with both approaches. Extra code may be required to observe tests
Software Engineering, COMP201 Slide 38
q
System demonstration
q
Test implementation
q
Test observation
Interface testing
q
q
q
Takes place when modules or sub-systems are integrated to create larger systems Objectives are to detect faults due to interface errors or invalid assumptions about interfaces Particularly important for object-oriented development as objects are defined by their interfaces
Software Engineering, COMP201
Slide 39
Interface testing
Test cases
A
B
C
Software Engineering, COMP201
Slide 40
Interfaces types
q
Parameter interfaces
Data passed from one procedure to another Block of memory is shared between procedures Sub-system encapsulates a set of procedures to be called by other sub-systems Sub-systems request services from other sub-systems
q
Shared memory interfaces
q
Procedural interfaces
q
Message passing interfaces
Software Engineering, COMP201
Slide 41
Interface errors
q
Interface misuse
A calling component calls another component and makes an error in its use of its interface e.g. parameters in the wrong order A calling component embeds assumptions about the behaviour of the called component which are incorrect The called and the calling component operate at different speeds and out-of-date information is accessed
q
Interface misunderstanding
q
Timing errors
Software Engineering, COMP201
Slide 42
Interface testing guidelines
q
q
q q q
Design tests so that parameters to a called procedure are at the extreme ends of their ranges Always test pointer parameters with null pointers Design tests which cause the component to fail Use stress testing in message passing systems In shared memory systems, vary the order in which components are activated
Software Engineering, COMP201 Slide 43
Stress testing
q
q
q
Exercises the system beyond its maximum design load. Stressing the system often causes defects to come to light Stressing the system test failure behaviour.. Systems should not fail catastrophically. Stress testing checks for unacceptable loss of service or data Particularly relevant to distributed systems which can exhibit severe degradation as a network becomes overloaded
Software Engineering, COMP201 Slide 44
Object-oriented testing
q
q
q
The components to be tested are object classes that are instantiated as objects Larger grain than individual functions so approaches to white-box testing have to be extended No obvious `top' to the system for top-down integration and testing
Software Engineering, COMP201
Slide 45
Testing levels
q q q q
Testing operations associated with objects Testing object classes Testing clusters of cooperating objects Testing the complete OO system
Software Engineering, COMP201
Slide 46
Object class testing
q
Complete test coverage of a class involves
Testing all operations associated with an object Setting and interrogating all object attributes Exercising the object in all possible states
q
Inheritance makes it more difficult to design object class tests as the information to be tested is not localised
Software Engineering, COMP201
Slide 47
Weather station object interface
WeatherStation identifier reportWeather () calibrate (instruments) test () startup (instruments) shutdown (instruments)
q q
q
Test cases are needed for all operat...