Introduction to Software...
Transcript of Introduction to Software...
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Introduction to Software Engineering(CS350)
Jongmoon Baik
Lecture 17
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Testing Conventional Applications
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Testability
• Operability—it operates cleanly• Observability—the results of each test case are readily
observed• Controllability—the degree to which testing can be
automated and optimized• Decomposability—testing can be targeted• Simplicity—reduce complex architecture and logic to
simplify tests• Stability—few changes are requested during testing• Understandability—of the design
James Bach, 1994
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What is a “Good” Test?
• A good test has a high probability of finding an error
• A good test is not redundant.• A good test should be “best of breed” • A good test should be neither too simple nor
too complex
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Internal and External Views
• Any engineered product (and most other things) can be tested in one of two ways: – Knowing the specified function that a product has
been designed to perform, tests can be conducted that demonstrate each function is fully operational while at the same time searching for errors in each function; [Black-box testing]
– Knowing the internal workings of a product, tests can be conducted to ensure that "all gears mesh," that is, internal operations are performed according to specifications and all internal components have been adequately exercised. [White-box testing]
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Test Case Design
"Bugs lurk in corners and congregate at boundaries ..."
Boris Beizer
OBJECTIVE
CRITERIA
CONSTRAINT
to uncover errors
in a complete manner
with a minimum of effort and time
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Exhaustive Testing
loop < 20 X
There are 10 possible paths! If we execute onetest per millisecond, it would take 3,170 years totest this program!!
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Selective Testing
loop < 20 X
Selected path
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Software Testing
Methods
Strategies
white-boxmethods
black-boxmethods
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Black-box test vs. White-box test
Black-box test
• Functional or behavioral testing
• Conducted at software interface
• Examines some fundamental aspect of a system
• Ignores internal logic of a software system
White-box test
• Glass-box or structural testing
• Uses knowledge of the internal structure of the software
• Examine procedural detail (logical paths and collaboration b/w components)
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White-Box Testing
... our goal is to ensure that all statements and conditions have been executed at least once ...
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Why Cover?
logic errors and incorrect assumptions are inversely proportional to a path's execution probability
we often believe that a path is not likely to be executed; in fact, reality is often counter intuitive
typographical errors are random; it's likely that untested paths will contain some
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Basis Path Testing
First, we compute the cyclomatic complexity:
number of simple decisions + 1 or
number of enclosed areas + 1
In this case, V(G) = 4
• A white-box testing technique• Enable to derive a logical complexity measure of a procedural design• Provide a guideline defining a basis set of execution paths• Guarantee to execute every statement in the program at once
ornumber of nodes – number of edges + 2
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Cyclomatic Complexity
A number of industry studies have indicated that the higher V(G), the higher the probability or errors.
V(G)
modules
modules in this range are more error prone
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Basis Path Testing
Next, we derive the independent paths:
Since V(G) = 4,there are four paths
Path 1: 1,2,3,6,7,8Path 2: 1,2,3,5,7,8Path 3: 1,2,4,7,8Path 4: 1,2,4,7,2,4,...7,8
Finally, we derive testcases to exercise these paths.
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Basis Path Testing Notes
you don't need a flow chart, but the picture will help when you trace program paths
count each simple logical test, compound tests count as 2 or more
basis path testing should be applied to critical modules
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Independent Paths?
• Any path through the program that introduces at least one new set of processing statements or a new condition
• Test can be designed to force execution of these paths (a basis set)
• Guaranteed to execute every statement at least once
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Cyclomatic Complexity
• A software metric that provides a quantitative measure of the logical complexity of a program
• Provides a single ordinal number (an upper bound for the number of tests to achieve a complete branch coverage
• Independent of language and language format • Extended to encompass the design and
structural complexity of a system
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Application Areas of CC
• Code development risk analysis.
• Change risk analysis in maintenance.
• Test Planning.
• Reengineering.
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Computation of CC
1. V(G), Cyclomatic Complexity= The number of regions in a flow graph, G
2. V(G) = E – N + 2Where E = No. of Edges and N = No. of Nodes
3. V(G) = P + 1Where P is the number of Predicated Nodes in a flow
graph, G
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Example: CC Computation
1. No. of Regions (R1,..,R4)V(G) = 4
2. V(G) = 11 Edges – 9 Nodes + 2 = 4
3. V(G) = 3 Predicate Nodes + 1 = 4
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2,3
6
87
4,5
9
10
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R1
R2
R3
R4
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Deriving Test Cases
• Summarizing:– Using the design or code as a foundation,
draw a corresponding flow graph.– Determine the cyclomatic complexity of the
resultant flow graph.– Determine a basis set of linearly independent
paths.– Prepare test cases that will force execution of
each path in the basis set.
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Graph Matrices
• A graph matrix is a square matrix whose size (i.e., number of rows and columns) is equal to the number of nodes on a flow graph
• Each row and column corresponds to an identified node, and matrix entries correspond to connections (an edge) between nodes.
• By adding a link weight to each matrix entry, the graph matrix can become a powerful tool for evaluating program control structure during testing
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Control Structure Testing
• Condition testing — a test case design method that exercises the logical conditions contained in a program module
• Data flow testing — selects test paths of a program according to the locations of definitions and uses of variables in the program
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Data Flow Testing• The data flow testing method [Fra93] selects test paths of a program
according to the locations of definitions and uses of variables in the program.– Assume that each statement in a program is assigned a unique
statement number and that each function does not modify its parameters or global variables. For a statement with S as its statement number
• DEF(S) = {X | statement S contains a definition of X}• USE(S) = {X | statement S contains a use of X}
– A definition-use (DU) chain of variable X is of the form [X, S, S'], where S and S' are statement numbers, X is in DEF(S) and USE(S'), and the definition of X in statement S is live at statement S'
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Data Flow Testing – Cont.
K
U
D
A
u
d
d
u, k
d, k
k
u
k, u, d
Data FlowAnomaly State
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Loop Testing
Nested Loops
ConcatenatedLoops Unstructured
Loops
Simple loop
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Loop Testing: Simple Loops
Minimum conditions—Simple Loops
1. skip the loop entirely
2. only one pass through the loop
3. two passes through the loop
4. m passes through the loop m < n
5. (n-1), n, and (n+1) passes through the loop
where n is the maximum number of allowable passes
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Loop Testing: Nested Loops
Start at the innermost loop. Set all outer loops to their minimum iteration parameter values.Test the min+1, typical, max-1 and max for the innermost loop, while holding the outer loops at their minimum values.Move out one loop and set it up as in step 2, holding all other loops at typical values. Continue this step until the outermost loop has been tested.
If the loops are independent of one another then treat each as a simple loopelse* treat as nested loops
endif* for example, the final loop counter value of loop 1 is used to initialize loop 2.
Nested Loops
Concatenated Loops
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Black-Box Testing
requirements
eventsinput
output
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Black-Box Testing
• How is functional validity tested?• How is system behavior and performance tested?• What classes of input will make good test cases?• Is the system particularly sensitive to certain input
values?• How are the boundaries of a data class isolated?• What data rates and data volume can the system
tolerate?• What effect will specific combinations of data
have on system operation?
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Graph-Based Methods
newfile
menu select generates(generation time < 1.0 sec)
documentwindow
documenttex
t
is represented ascontains
Attributes:
background color: whitetext color: default color
or preferences
(b)
object#1
Directed link(link weight)
object#2
object#3
Undirected link
Parallel links
Node weight(value
)
(a)
allows editingof
To understand the objects that are modeled in software and the relationships that connect these objects
In this context, we consider the term “objects” in the broadest possible context. It encompasses data objects, traditional components (modules), and object-oriented elements of computer software.
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Equivalence Partitioning
userqueries
mousepicks
outputformats
prompts
FKinput
data
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Sample Equivalence Classes
user supplied commandsresponses to system promptsfile namescomputational data
physical parameters bounding valuesinitiation values
output data formattingresponses to error messagesgraphical data (e.g., mouse picks)
data outside bounds of the program physically impossible dataproper value supplied in wrong place
Valid data
Invalid data
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Boundary Value Analysis
userqueries mouse
picks
outputformats
prompts
FKinput
data
outputdomaininput domain
• Focus on selecting a set of test cases that exercise bounding values– Select test cases at the edges of the class
• Complementary to Equivalence Partitioning• Derive test cases from output domain as well
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Comparison Testing
• Used only in situations in which the reliability of software is absolutely critical (e.g., human-rated systems)– Separate software engineering teams develop
independent versions of an application using the same specification
– Each version can be tested with the same test data to ensure that all provide identical output
– Then all versions are executed in parallel with real-time comparison of results to ensure consistency
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Orthogonal Array Testing• Used when the number of input
parameters is small and the values that each of the parameters may take are clearly bounded
One input item at a time L9 orthogonal array
XY
Z
XY
Z
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Model-Based Testing• Analyze an existing behavioral model for the software or create one.
– Recall that a behavioral model indicates how software will respond to external events or stimuli.
• Traverse the behavioral model and specify the inputs that will force the software to make the transition from state to state. – The inputs will trigger events that will cause the transition to occur.
• Review the behavioral model and note the expected outputs as the software makes the transition from state to state.
• Execute the test cases.• Compare actual and expected results and take corrective action as
required.
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Software Testing Patterns
• Testing patterns are described in much the same way as design patterns (Chapter 12).
• Example:• Pattern name: ScenarioTesting• Abstract: Once unit and integration tests have been
conducted, there is a need to determine whether the software will perform in a manner that satisfies users. The ScenarioTesting pattern describes a technique for exercising the software from the user’s point of view. A failure at this level indicates that the software has failed to meet a user visible requirement. [Kan01]
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Q & A