Лекция 6: Test-Case Design
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What is a Test?
Test Oracle:
To verify the execution is correct, we need to compare the
actual outcome with the expected outcome.
Test oracle is a tool that can return the expected outcome
for a given input vector.
An executable specification of a program can be used as a
test oracle for that program.
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White box testing
Syntactic abstraction of source code.
Test cases are determined from the implementation of
the software.
White box testing: flow graphs
◦ control flow testing
◦ data flow testing.
Purpose of white box test case generation: Coverage of
the flow graph in accordance with one or more test
criteria.
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Control Flow Testing
Control flow testing uses the control structure of a
program to develop the test cases for the program.
The test cases are developed to sufficiently cover the
whole control structure of the program.
The control structure of a program can be represented
by the control flow graph of the program.
The control flow graph G = (N, E) of a program consists
of a set of nodes N and a set of edge E.
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Control Flow Graph
Each node represents a set of program statements:
◦ A decision node contains a conditional statement
that creates 2 or more control branches (e.g. if or
switch statements).
◦ A merge node usually does not contain any
statement and is used to represent a program point
where multiple control branches merge.
◦ A statement node contains a sequence of
statements. The control must enter from the first
statement and exit from the last statement.
There is an edge from node n1to node n2 if the control
may flow from the last statement in n1 to the first
statement in n2.
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Control Flow Graph: An
Example
6
Test Cases
A test case is a complete path from the entry node
to the exit node of a control flow graph.
A test coverage criterion measures the extent to
which a set of test cases covers a program:
◦ Statement coverage (SC) – node coverage
◦ Decision coverage (DC) – edge coverage
◦ Condition coverage (CC)
◦ Decision/condition coverage (D/CC)
◦ Multiple condition coverage (MCC)
◦ Path coverage (PC)
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Test Case
Test case: {𝑖 ∈ 𝐷, 𝑜 ∈ 𝑂}
Test suite: set of test cases
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Statement Coverage
Every
statement in
the program has
been executed at
least once.
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Decision Coverage
Every
statement in
the program has
been executed
at least once,
and every
decision in the
program has
taken all
possible
outcomes at
least once.
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Example
public void foo(int a, int b,
int x) {
if (a>1 && b==0) {
x=x/a;
}
if (a==2 || x>1) {
x=x+1;
}
}
Decision coverage:
1.ace and abd
2.acd and abe
А = 3, В = 0, X = 3
А = 2, В = 1, и X = 1
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Condition Coverage
Every statement in the program has been executed at
least once, and every condition in each decision has
taken all possible outcomes at least once.
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Example
Condition Coverage
four conditions:
A>1, B=0, A=2, and X>1
point a:
A>1, A<=1, B=0, and B<>0
point b:
A=2, A<>2, X>1, and X<=1
Test cases:
◦ ace: A=2, B=0, X=4
◦ adb: A=1, B=1, X=1
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Decision/Condition Coverage
Every statement in the program has been executed at
least once, every decision in the program has taken all
possible outcomes at least once, and every condition
in each decision has taken all possible outcomes at least
once.
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Multiple Condition Coverage
Every statement in the
program has been executed at
least once, all possible
combination of condition
outcomes in each decision
has been invoked at least
once.
There are 2n combinations of
condition outcomes in a
decision with n conditions.
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Example
Test cases must cover eight
combinations:
Test-case input values, and the
combinations they cover, are as
follows:
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Path Coverage
Every complete path in the program has been
executed at least once.
A loop usually has an infinite number of complete
paths.
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White-box: loop testing
Statement and branch coverage are not sufficient
Single loop strategy:
◦ Zero iterations
◦ One iteration
◦ Two iterations
◦ Typical number of iterations
◦ n-1, n, and n+1 iterations (n maximum number of allowable
◦ iterations)
Nested loop strategy:
◦ Single loop strategy often intractable
◦ Select minimum values for outer loop(s)
◦ Treat inner loop as a single loop
◦ Work ‘outwards’ and choose typical values for inner loops
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Path Selection
It is better to take many simple paths than a few
complicated ones.
There is no harm in taking paths that will exercise the
same code more than once.
Select paths as small variations of previous paths.
Try to change one thing in each path at a time.
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Example
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