preliminaries-raytheon.ppt introductione

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1. Software Testing
Part I: Preliminaries
Aditya P. Mathur
Purdue University
July 20-24, 1998
@ Raytheon Technical Services Company
Indianapolis.
Graduate Assistants: Joao Cangussu
Sudipto Ghosh
Priya Govindrajan
Last update: July 15, 1998

2. Software Testing: Preliminaries 2
Class schedule
Monday-Thursday July 20-23
–8-9:15amLecture session 1/Quiz
–9:15-9:30amBreak
–9:30-10:45amLecture session 2
–10:45-11amBreak
–11-12noonLecture session 3
–12-1pm Lunch
–1-5pm Lab session (breaks as needed)

3. Software Testing: Preliminaries 3
Class schedule-continued
Friday July 24
–8-8:30am Review and Q&A
–8:30-10am Final examination
–10-10:15am Break
–10:15-12noon SERT review
–12-1pm Lunch

4. Software Testing: Preliminaries 4
Class schedule-continued
Friday July 24
–1-2pm Lab session
–2-3pm Week 10 and SERT
feedback
–3pm Classes end...prepare for
the banquet!

5. Software Testing: Preliminaries 5
Course Organization
Part I: Preliminaries
Part II:Functional Testing
Part III:Test Assessment and
improvement
Part IV:Special Topics

6. Software Testing: Preliminaries 6
Text and supplementary reading
The craft of software testing by Brian
Marick, Prentice Hall, 1995.
Reading:
–A data-flow oriented program testing strategy,
J. W. Laski and B. Korel, IEEE Transactions on
Software Engineering, VOL. SE-9, NO. 3, May
1983, pp 347-354.

7. Software Testing: Preliminaries 7
Text and supplementary reading
–The combinatorial approach to automatic test
data generation, D. Cohen et al., IEEE
Software, VOL. 13, NO. 5, September 1996, pp
83-87.
–Comparing the error detection effectiveness of
mutation and data flow testing, in your notes,
part III.

8. Software Testing: Preliminaries 8
Text and supplementary reading
Effect of test set minimization on the fault
detection effectiveness of the all-uses
criterion, in your notes, part III.
Effect of test set size and block coverage on
the fault detection effectiveness, in your
notes, part III.

9. Software Testing: Preliminaries 9
Evaluation-Lectures
Quiz I: Preliminaries:
8:30-9am 7/21/98 10 points
Quiz II: Functional testing:
8:30-9am 7/22/98 10 points
Quiz III: Test assessment:
8:30-9am 7/23/98 10 points
Final Exam: Comprehensive:
10:30-12noon7/24/98 25points
Total lectures: 55%

10. Software Testing: Preliminaries 10
Evaluation-Laboratories
Lab 1:7/20/98 10%
Lab 2:7/21/98 10%
Lab 3:7/22/98 15%
Lab 4:7/23/98 10%
Total labs: 45%
Total testing course:lectures+labs.=100%

11. Software Testing: Preliminaries 11
Part I: Preliminaries
Learning Objectives
What is testing? How does it differ from
verification?
How and why does testing improve our
confidence in program correctness?
What is coverage and what role does it play in
testing?
What are the different types of testing?

12. Software Testing: Preliminaries 12
Testing: Preliminaries
What is testing?
–The act of checking if a part or a product
performs as expected.
Why test?
–Gain confidence in the correctness of a part or a
product.
–Check if there are any errors in a part or a
product.

13. Software Testing: Preliminaries 13
What to test?
During software lifecycle several products
are generated.
Examples:
–Requirements document
–Design document
–Software subsystems
–Software system

14. Software Testing: Preliminaries 14
Test all!
Each of these products needs testing.
Methods for testing various products are
different.
Examples:
–Test a requirements document using scenario
construction and simulation
–Test a design document using simulation.
–Test a subsystem using functional testing.

15. Software Testing: Preliminaries 15
What is our focus?
We focus on testing programs.
Programs may be subsystems or complete
systems.
These are written in a formal programming
language.
There is a large collection of techniques and
tools to test programs.

16. Software Testing: Preliminaries 16
Few basic terms
Program:
–A collection of functions, as in C, or a
collection of classes as in java.
Specification
–Description of requirements for a program. This
might be formal or informal.

17. Software Testing: Preliminaries 17
Few basic terms-continued
Test case or test input
–A set of values of input variables of a program.
Values of environment variables are also
included.
Test set
–Set of test inputs
Program execution
–Execution of a program on a test input.

18. Software Testing: Preliminaries 18
Few basic terms-continued
Oracle
–A function that determines whether or not the
results of executing a program under test is as
per the program’s specifications.

19. Software Testing: Preliminaries 19
Correctness
Let P be a program (say, an integer sort
program).
Let S denote the specification for P.
For sort let S be:

20. Software Testing: Preliminaries 20
Sample Specification
–P takes as input an integer N>0 and a sequence
of N integers called elements of the sequence.
–Let K denote any element of this sequence,
–P sorts the input sequence in descending order
and prints the sorted sequence.
. )1(0 somefor eeK 

21. Software Testing: Preliminaries 21
Correctness again
P is considered correct with respect to a
specification S if and only if:
–For each valid input the output of P is in
accordance with the specification S.

22. Software Testing: Preliminaries 22
Errors, defects, faults
Error: A mistake made by a programmer
Example: Misunderstood the requirements.
Defect/fault: Manifestation of an error in a
program.
Example:
Incorrect code: if (a<b) {foo(a,b);}
Correct code: if (a>b) {foo(a,b);}

23. Software Testing: Preliminaries 23
Failure
Incorrect program behavior due to a fault in
the program.
Failure can be determined only with respect
to a set of requirement specifications.
A necessary condition for a failure to occur is
that execution of the program force the
erroneous portion of the program to be
executed. What is the sufficiency condition?

24. Software Testing: Preliminaries 24
Errors and failure
Program
Inputs
Error-revealing
inputs cause
failure
Outputs
Erroneous
outputs indicate
failure

25. Software Testing: Preliminaries 25
Debugging
Suppose that a failure is detected during the
testing of P.
The process of finding and removing the cause
of this failure is known as debugging.
The word bug is slang for fault.
Testing usually leads to debugging
Testing and debugging usually happen in a
cycle.

26. Software Testing: Preliminaries 26
Test-debug cycle
Test
Debug
Failure?
Testing
complete?
Done!
Yes
No
Yes No

27. Software Testing: Preliminaries 27
Testing and code inspection
Code inspection is a technique whereby the
source code is inspected for possible errors.
Code inspection is generally considered
complementary to testing. Neither is more
important than the other!
One is not likely to replace testing by code
inspection or by verification.

28. Software Testing: Preliminaries 28
Testing for correctness?
Identify the input domain of P.
Execute P against each element of the input
domain.
For each execution of P, check if P
generates the correct output as per its
specification S.

29. Software Testing: Preliminaries 29
What is an input domain ?
Input domain of a program P is the set of all
valid inputs that P can expect.
The size of an input domain is the number
of elements in it.
An input domain could be finite or infinite.
Finite input domains might be very large!

30. Software Testing: Preliminaries 30
Identifying the input domain
For the sort program:
N: size of the sequence, K: each element of
the sequence.
–Example: For N<3, e=3, some sequences in the
input domain are:
[ ]: An empty sequence (N=0).
[0]: A sequence of size 1 (N=1)
[2 1]:A sequence of size 2 (N=2).

31. Software Testing: Preliminaries 31
Size of an input domain
Suppose that
The size of the input domain is the number
of all sequences of size 0, 1, 2, and so on.
The size can be computed as:
6
100 N
. somefor )1(0 eeK 


6
10
0i
i
e

32. Software Testing: Preliminaries 32
Testing for correctness? Sorry!
To test for correctness P needs to be
executed on all inputs.
For our example, it will take several light
years to execute a program on all inputs on
the most powerful computers of today!

33. Software Testing: Preliminaries 33
Exhaustive Testing
This form of testing is also known as
exhaustive testing as we execute P on all
elements of the input domain.
For most programs exhaustive testing is not
feasible.
What is the alternative?

34. Software Testing: Preliminaries 34
Verification
Verification for correctness is different
from testing for correctness.
There are techniques for program
verification which we will not discuss.

35. Software Testing: Preliminaries 35
Partition Testing
In this form of testing the input domain is
partitioned into a finite number of sub-
domains.
P is then executed on a few elements of
each sub-domain.
Let us go back to the sort program.

36. Software Testing: Preliminaries 36
Sub-domains
Suppose that and e=3. The size of
the partitions is :
We can divide the input
domain into three
sub-domains as shown.
133333
210
2
0

i
i
20 N
1
2
3
0N
2N
1N

37. Software Testing: Preliminaries 37
Fewer test inputs
Now sort can be tested on one element
selected from each domain.
For example, one set of three inputs is:
[ ]Empty sequence from sub-domain 1.
[2]Sequence from sub-domain 2.
[2 0]Sequence from sub-domain 3.
We have thus reduced the number of inputs
used for testing from 13 to 3!

38. Software Testing: Preliminaries 38
Confidence in your program
Confidence is a measure of one’s belief in
the correctness of the program.
Correctness is not measured in binary
terms: a correct or an incorrect program.
Instead, it is measured as the probability of
correct operation of a program when used in
various scenarios.

39. Software Testing: Preliminaries 39
Measures of confidence
Reliability: Probability that a program will
function correctly in a given environment
over a certain number of executions.
We do not plan to cover Reliability.
Test completeness: The extent to which a
program has been tested and errors found
have been removed.

40. Software Testing: Preliminaries 40
Example: Increase in Confidence
We consider a non-programming example
to illustrate what is meant by “increase in
confidence.”
Example: A rectangular field has been
prepared to certain specifications.
–One item in the specifications is:
“There should be no stones remaining in the field.”

41. Software Testing: Preliminaries 41
Rectangular Field
X
Y
Search for stones inside the rectangle.
0 L
W

42. Software Testing: Preliminaries 42
Organizing the search
We divide the entire field into smaller
search rectangles.
The length and breadth of each search
rectangle is one half that of the smallest
stone.

43. Software Testing: Preliminaries 43
Testing the rectangular field
The field has been prepared and our task is
to test it to make sure that it has no stones.
How should we organize our search?

44. Software Testing: Preliminaries 44
Partitioning the field
We divide the entire field into smaller
search rectangles.
The length and breadth of each search
rectangle is one half that of the smallest
stone.

45. Software Testing: Preliminaries 45
Partitioning into search
rectangles
12 345 6 7
1
2
3
4
5
6
7
8
X
Y
Stone
W
i
d
t
h
Length

46. Software Testing: Preliminaries 46
Input domain
Input domain is the set of all possible inputs
to the search process.
In our example this is the set of all points in
the field. Thus, the input domain is infinite!
To reduce the size of the input domain we
partition the field into finite size rectangles.

47. Software Testing: Preliminaries 47
Rectangle size
The length and breadth of each search
rectangle is one half that of the smallest
stone.
This ensures that each stone covers at least
one rectangle. (Is this always true?)

48. Software Testing: Preliminaries 48
Constraints
Testing must be completed in less than H
hours.
Any stone found during testing is removed.
Upon completion of testing the probability
of finding a stone must be less than p.

49. Software Testing: Preliminaries 49
Number of search rectangles
Let
L: Length of the field
W:Width of the field
l:Length of the smallest stone
w:Width of the smallest stone
Size of each rectangle: l/2 x w/2
Number of search rectangles (R)=(L/l)*(W/w)*4

Assume that L/l and W/w are integers.

50. Software Testing: Preliminaries 50
Time to test
Let t be the time to look inside one search
rectangle. No rectangle is examined more than
once.
Let o be the overhead in moving from one
search rectangle to another.
Total time to search (T)=R*t+(R-1)*o
Testing with R rectangles is feasible only if
T<H.

51. Software Testing: Preliminaries 51
Partitioning the input domain
This set consists of all search rectangles (R).
Number of partitions of the input domain is
finite (=R).
However, if T>H then the number of
partitions is is too large and scanning each
rectangle once is infeasible.
What should we do in such a situation?

52. Software Testing: Preliminaries 52
Option 1: Do a limited search
Of the R search rectangles we examine only
r where r is such that (t*r+o*(r-1)) < H.
This limited search will satisfy the time
constraint.
Will it satisfy the probability constraint?

53. Software Testing: Preliminaries 53
Distribution of stones
To satisfy the probability constraint we
must scan enough search rectangles so that
the probability of finding a stone, after
testing, remains less than p.
Let us assume that
–there are stones remaining after i test
cycles.
i
s
ii
Rs

54. Software Testing: Preliminaries 54
Distribution of stones
–There are search rectangles remaining after i
test cycles.
–Stones are distributed uniformly over the field
–An estimate of the probability of finding a
stone in a randomly selected remaining search
rectangle is
iii
Rsp /
i
R

55. Software Testing: Preliminaries 55
Probability constraint
We will stop looking into rectangles if
Can we really apply this test method in
practice?
pp
i


56. Software Testing: Preliminaries 56
Confidence
Number of stones in the field is not known in
advance.
Hence we cannot compute the probability of
finding a stone after a certain number of
rectangles have been examined.
The best we can do is to scan as many
rectangles as we can and remove the stones
found.

57. Software Testing: Preliminaries 57
Coverage
After a rectangle has been scanned for a
stone and any stone found has been
removed, we say that the rectangle has been
covered.
Suppose that r rectangles have been
scanned from a total of R. Then we say that
the coverage is r/R.

58. Software Testing: Preliminaries 58
Coverage and confidence
What happens when coverage increases?
As coverage increases so does our
confidence in a “stone-free” field.
In this example, when the coverage reaches
100%, all stones have been found and
removed. Can you think of a situation when
this might not be true?

59. Software Testing: Preliminaries 59
Option 2: Reduce number of partitions
If the number of rectangles to scan is too
large, we can increase the size of a
rectangle. This reduces the number of
rectangles.
Increasing the size of a rectangle also
implies that there might be more than one
stone within a rectangle.

60. Software Testing: Preliminaries 60
Rectangle size
As a stone may now be smaller than a
rectangle, detecting a stone inside a
rectangle is not guaranteed.
Despite this fact our confidence in a “stone-
free” field increases with coverage.
However, when the coverage reaches100%
we cannot guarantee a “stone-free” field.

61. Software Testing: Preliminaries 61
Coverage vs. Confidence
Coverage
C
o
n
f
i
d
e
n
c
e
1(=100%)
1
0
Does not imply that the field
is “stone-free”.

62. Software Testing: Preliminaries 62
Rectangle size
Rectangle size
p=Probability of detecting a stone inside a
rectangle, given that the stone is there.
t=time to complete a test.
small large
t, p

63. Software Testing: Preliminaries 63
Analogy
Field:Program
Stone:Error
Scan a rectangle:Test program on one input
Remove stone:Remove error
Partition:Subset of input domain
Size of stone:Size of an error
Rectangle size:Size of a partition

64. Software Testing: Preliminaries 64
Analogy…continued
Size of an error is the number of inputs in the input domain
each of which will cause a failure due to that error.
Inputs that
cause failure
due to Error 1
Inputs that cause
failure due to
Error 2.
Error 1 is larger
than Error 2.
Input domain

65. Software Testing: Preliminaries 65
Confidence and probability
Increase in coverage increases our
confidence in a “stone-free” field.
It might not increase the probability that the
field is “stone-free”.
Important: Increase in confidence is NOT
justified if detected stones are not
guaranteed to be removed!

66. Software Testing: Preliminaries 66
Types of testing
Source of clues for
test input construction
Object under test
Basis for
classification
All of these methods can be
applied here.

67. Software Testing: Preliminaries 67
Testing: based on source of test inputs
Functional testing/specification
testing/black-box testing/conformance
testing:
–Clues for test input generation come from
requirements.
White-box testing/coverage testing/code-
based testing
–Clues come from program text.

68. Software Testing: Preliminaries 68
Testing: based on source of test inputs
Stress testing
–Clues come from “load” requirements. For
example, a telephone system must be able to
handle 1000 calls over any 1-minute interval.
What happens when the system is loaded or
overloaded?

69. Software Testing: Preliminaries 69
Testing: based on source of test inputs
Performance testing
–Clues come from performance requirements. For
example, each call must be processed in less than
5 seconds. Does the system process each call in
less than 5 seconds?
Fault- or error- based testing
–Clues come from the faults that are injected into
the program text or are hypothesized to be in the
program.

70. Software Testing: Preliminaries 70
Testing: based on source of test inputs
Random testing
–Clues come from requirements. Test are
generated randomly using these clues.
Robustness testing
–Clues come from requirements. The goal is to
test a program under scenarios not stipulated in
the requirements.

71. Software Testing: Preliminaries 71
Testing: based on source of test inputs
OO testing
–Clues come from the requirements and the
design of an OO-program.
Protocol testing
–Clues come from the specification of a protocol.
As, for example, when testing for a
communication protocol.

72. Software Testing: Preliminaries 72
Testing: based on item under test
Unit testing
Testing of a program unit. A unit is the smallest
testable piece of a program. One or more units
form a subsystem.
Subsystem testing
–Testing of a subsystem. A subsystem is a
collection of units that cooperate to provide a
part of system functionality

73. Software Testing: Preliminaries 73
Testing: based on item under test
Integration testing
–Testing of subsystems that are being integrated
to form a larger subsystem or a complete
system.
System testing
–Testing of a complete system.

74. Software Testing: Preliminaries 74
Testing: based on item under test
Regression testing
–Test a subsystem or a system on a subset of the
set of existing test inputs to check if it
continues to function correctly after changes
have been made to an older version.
And the list goes on and on!

75. Software Testing: Preliminaries 75
Test input construction and objects under test
Test object
S
o
u
r
c
e

o
f
c
l
u
e
s
f
o
r

t
e
s
t
i
n
p
u
t
s
unit subsystem system
Requirements
Code

76. Software Testing: Preliminaries 76
Summary: Terms
Testing and debugging
Specification
Correctness
Input domain
Exhaustive testing
Confidence

77. Software Testing: Preliminaries 77


Summary: Terms
Reliability
Coverage
Error, defect, fault, failure
Debugging, test-debug cycle
Types of testing, basis for classification

78. Software Testing: Preliminaries 78
Summary: Questions
What is the effect of reducing the partition
size on probability of finding errors?
How does coverage effect our confidence in
program correctness?
Does 100% coverage imply that a program
is fault-free?
What decides the type of testing?