White box testing-200709

White Box Testing
Len Schroath
September 18, 2007

Agenda
• White-box vs Black-box
• Program Flow Controls
• White-box Test Methods
• Exercises
• Complexity
• Q&A

What is White-box Testing?
• Looking at the internal structure of a program
and deriving test cases based on the logic or
control flow.
• Test cases can be designed to reach every
branch in the code and to exercise each
condition
• Typically done during unit testing
• Also known as:
– Structural Testing
– Glass-Box Testing

What is Black-box Testing?
• Looking at the program from an external
point of view and deriving test cases
based on the specification.
• The only criteria upon which the program
is judged is if it produces the correct
output for a given input.

Why Do Both?
Black-box
• Impossible to write a test
case for every possible
set of inputs and outputs
• Some of the code may
not be reachable without
extraordinary measures
• Specifications are not
always complete
White-box
• Does not address the
question of whether or
not the program matches
the specification
• Does not tell you if all of
the functionality has been
implemented
• Does not discover
missing program logic

Basic Program Flow Controls
• IF
• IF-Then-Else
• FOR
• While
• Do-While
• Case

Example Control Flow Graph
Source: The Art of Software Testing – Glenford Myers

Exercise #1
• int main (int argc, char *argv[])
• {
• /* Process CTRL-C Interrupts */
• signal(SIGINT,catcher);
• if (validate_command_line(argc)) return(1);
• if (job_initialize(argv)) return(1);
• processTestList(); /* Process all testCases in
TestList */
• displayResults();
• fprintf(stdout,"Test Completen");
• job_termination();
• return(0);
• } /* main */ Can you diagram
this code?

Did You Get Something Like This?

Exercise #2
/* Attempt Statusreadback - log SRB data to logFile */
int process_srb(void)
{
int srb_count = 0;
do
{
srb_count = read_printer(srb_in);
} while (!srb_count);
fprintf(logFile,"%sn",srb_in);
return(srb_count);
} /* process_srb */
/* Write String to Printer via Parallel or Serial port */
void write_printer (char *outputline)
{
if (strstr(printertype,"PAR") != NULL)
{
bwrite_parST(printerport,outputline);
}
else if (strstr(printertype,"SER") != NULL)
{
bwwrite_serial(printerport,outputline,strlen(outputline));
}
else if (strstr(printertype, "FILE") !=NULL)
{
fprintf(printerFile,"%s",outputline);
}
} /* write_printer */
Can you diagram
this code?

White-box Test Methods
• Statement Coverage
• Decision/Branch Coverage
• Condition Coverage
• Decision/Condition Coverage
• Path Coverage

Example Code Fragment
• If ((A>1) & (B=0))
then Do;
• X=X/A;
• END;
• If ((A==2) | (X>1))
then Do;
• X=X+1;
• END;
• END;

Statement Coverage
• Exercise all
statements at least
once
• How many test
cases?
A=2 and B=0 (ace)

Decision/Branch Coverage
• Each decision has a
true and a false
outcome at least once
• How many test
cases?
A=2 and B=0 (ace)
A=1 and X=1 (abd)

Condition Coverage
• Each condition in a
decision takes on all
possible outcomes at
least once
• Conditions: A>1, B=0,
A=2, X>1
• How many test cases?
A=2, B=0, and X=4 (ace)
A=1, B=1, and X=1 (abd)

Decision/Condition Coverage
• Each condition in a decision
takes on all possible
outcomes at least once, and
each decision takes on all
possible outcomes at least
once
• How many test cases?
 A=2, B=0, and X=4 (ace)
 A=1, B=1, and X=1 (abd)
• What about these?
 A=1, B=0, and X=3
 A=2, B=1, and X=1
(abe)
(abe)

Multiple Condition Coverage
• Exercise all possible
combinations of
condition outcomes in
each decision
• Conditions:
A>1, B=0
A>1, B<>0
A<=1, B=0
A<=1, B<>0
A=2, X>1
A=2, X<=1
A<>2, X>1
A<>2, X<=1

Multiple Condition Coverage
• How many test
cases?
A=2, B=0, X=4
A=2, B=1, X=1
A=1, B=0, X=2
A=1, B=1, X=1
(ace)
(abe)
(abe)
(abd)

Path Coverage
• Every unique path
through the program
is executed at least
once
• How many test
cases?
A=2, B=0, X=4 (ace)
A=2, B=1, X=1 (abe)
A=3, B=0, X=1 (acd)
A=1, B=1, X=1 (abd)

McCabe’s Cyclomatic Complexity
• Software metric
• Developed by Tom McCabe (circa 1976)
• Directly measures the number of linearly
independent paths through a program’s
source code, taking into account the
various decision points
• Independent of implementation language
Source: Wikipedia

How Complex Should Code Be?
• <10: Simple module, not much risk
• 10-20: More Complex; moderate risk
• 20-50: Complex; high risk
• >50: Untestable; extremely high risk
Source: Carnegie Mellon Software Engineering Institute

Complexity Caveats
• As code is broken into smaller modules to
decrease cyclomatic complexity, structural
complexity increases
• Some modules may have high complexity
but are very easy to comprehend and
easy to test
• High complexity numbers are only an
indicator of something to investigate

White box testing-200709

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