CS 325: Software Engineering
Lesson Twenty
Software Testing
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Black-Box Testing
White-Box Testing
Regression Testing
Black-Box Testing
Recall that black-box testing is used to determine whether a
software system meets its functional specifications.
Black-box testing comes in multiple flavors:
Equivalence Partitioning
Divide the input and output domains into disjoint
subsets and test one selection from each subset
Boundary Value Analysis
Set up the Equivalence Partitioning subsets;
test selections at and near their boundaries
Cause-Effect Analysis
Map the different combinations
of system input values to their
corresponding resultant output
values
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Lesson Twenty
Software Testing
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Black-Box Testing:
Equivalence Partitioning
For the function below, equivalence partitioning would
involve three input pairs: one producing overflow, one
producing underflow, and one producing neither.
int safe_add( int a, int b )
{
int c = a + b;
if ( (a >= 0) && (b >= 0) && (c < 0) )
cout << "ERROR: Overflow!\n" );
else if ( (a < 0) && (b < 0) && (c >= 0) )
cout << "ERROR: Underflow!\n" );
return c;
}
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Lesson Twenty
Software Testing
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Black-Box Testing:
Boundary-Value Analysis
For the function below, boundary values would be
where a+b=INT_MAX and where a+b=INT_MIN, while
values just beyond the boundaries would be where
a+b=INT_MAX+1 an d where a+b=INT_MIN-1.
int safe_add( int a, int b )
{
int c = a + b;
if ( (a >= 0) && (b >= 0) && (c < 0) )
cout << "ERROR: Overflow!\n" );
else if ( (a < 0) && (b < 0) && (c >= 0) )
cout << "ERROR: Underflow!\n" );
return c;
}
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Lesson Twenty
Software Testing
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Black-Box Testing:
Cause-Effect Analysis
Consider a loan application software system, where users can enter the
amount of the monthly repayment or the number of years they want to
take to pay back the loan (i.e., the term of the loan). If a user enters both,
the system will make a compromise between the two if they conflict.
The two conditions are the loan amount and the term, which are put in a
table, along with their different combinations of possible values.
Conditions
Rule 1
Rule 2
Rule 3
Rule 4
Repayment amount has been entered
T
T
F
F
Term of loan has been entered
T
F
T
F
Outcome: Process loan amount
Y
Y
Outcome: Process term
Y
Y
Outcome Error message
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Software Testing
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Test cases would then be developed to
test all four of the cause-effect rules.
Y
Black-Box Testing:
Cause-Effect Analysis (continued)
Consider a credit card system that offers discounts.
New customers who want to open a credit card account will get a 15%
discount on the day they open their accounts.
Existing customers who hold a loyalty card, always get a 10% discount.
Finally, customers who have a coupon, can get 20% off today (but this
coupon discount can’t be used with the ‘new customer’ discount).
Discount amounts are added, if applicable.
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Lesson Twenty
Software Testing
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Conditions
Rule 1
Rule 2
Rule 3
Rule 4
Rule 5
Rule 6
Rule 7
Rule 8
New customer (15%)
T
T
T
T
F
F
F
F
Loyalty card (10%)
T
T
F
F
T
T
F
F
Coupon (20%)
T
F
T
F
T
F
T
F
Effect: Discount
NA
NA
20%
15%
30%
10%
20%
0%
Note that Rules 1 and 2 represent impossible cases (new customers
with loyalty cards). Also, Rule 3 assumes that customers always
select the larger discount (when they have to select).
White-Box Testing
White-box testing derives test cases via knowledge of the
source code itself.
Essentially, the minimum number of test cases needed for
white-box testing is the number of distinct paths from the
start to the finish of the code (with loops being traversed
no more than once).
This number is called the cyclomatic
complexity of the program.
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Lesson Twenty
Software Testing
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White-Box Testing:
Cyclomatic Complexity
Consider the various
paths to implement the
following rule in the
game Monopoly.
If a player lands on a property
owned by an opponent, the
player needs to pay the rent. If
the player doesn’t have enough
money, the player is out of the
game. If the property is not
owned, and the player has
enough money, the player may
buy the property for the price
associated with the property.
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Software Testing
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White-Box Testing:
Cyclomatic Complexity (continued)
There are six independent paths through this code:
1. 1-2-3-4-5-10 (property owned by others, no money for rent)
2. 1-2-3-4-6-10 (property owned by others, pay rent)
3. 1-2-3-10 (property owned by the player)
4. 1-2-7-10 (property available, don’t have enough money)
5. 1-2-7-8-10 (property available, have money, don’t want to buy it)
6. 1-2-7-8-9-10 (property available, have money, and buy it)
So, the minimum
number of test cases
needed to test this
would be six.
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Software Testing
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Regression Testing
When features are added or altered, the changes might
cause previously working code to fail
Common methods of regression testing include rerunning previously run tests and checking whether
previously fixed bugs have reemerged
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Lesson Twenty
Software Testing
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