CSE1301 Computer Programming: Lecture 12 Debugging and Testing

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CSE1301 Computer Programming Lecture
12Debugging and Testing
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Topics

• How to find errors in your program?
• Methods for debugging
• Methods for testing

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Debugging Basics

• Know the (C) language well.

Examples
float x, y, z 3.5
printf(d\n, num)
scanf(f, x)
scanf(s, name)
if (i lt N) scanf(d\n, i)
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Debugging Basics (cont.)

• Pay attention to compiler error and warning
  messages.

Examples
Possible incorrect assignment.
if (ch Q) break
Possible use of N before declaration.
scanf(d, N)
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Tracing

• Trace execution of program
• location in the program
• status/contents of variables
• Tools
• programming environment
• eg. step, breakpoints, watch
• debugging statements
• eg. output values of variables, markers at
  specific locations, etc.

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Example Debugging Statements
int debugging 1 ... for (i0 iltN
i) scanf(s, name) if (debugging)
printf("for id, names\n", i,
name)
TIP make debugging statements conditional on a
boolean variable.
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Methods for Testing

• Test data set should fully test program.
• Every line of code is executed at least once
  (i.e., all logical paths of program are
  traversed).
• Use the design, represented by flow diagram.

TIP build your programs incrementally, testing
small components as you go along.
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Example BestMark (Alg 9)

• module getNextMark
• input nextMark
• return nextMark

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Classes of Test data

• Valid data
• Valid boundary data
• Special or unusual cases
• Invalid data

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Test Data Valid Data

• What would valid data be?
• What does it depend on?
• Example BestMark
• What the test is out of?
• If mark is out of 100 valid test data
• 75, 65, 55.

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Test Data Valid Boundary Data

• What are the extremes?
• Example BestMark
• minimum of 0
• maximum of 100
• Test selection conditions
• Test iteration exit conditions
• Test first and last elements of an array (lecture
  23)

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Test Data Special Cases

• Example BestMark
• What if someone is absent or the mark is withheld
  (special consideration)?

loop input nextMark if nextMark is Abs''
or WH'' output No mark for this
student'' else return nextMark
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Test Data Invalid Data

• What is invalid data?
• Incorrect type of data.
• Data not in expected range.
• Use features of the programming language to
  ensure correct data type.
• Example BestMark
• mark can be restricted to an integer
• int mark
• scanf(d, mark)

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Test Data Invalid Data (cont.)

• loop
• input nextMark
• if nextMark is Abs'' or WH''
• output No mark for this student''
• else if nextMark lt 0 or nextMark gt 100
• output invalid mark not 0 - 100''
• else
• return nextMark

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Example

• int x,y
• scanf("d d", x, y)
• if (x gt 2)
• while (x gt y)
• printf("S1,")
• x--
• printf("S2,")
• else if (x lt y)
• printf("S3,")
• printf("S4")

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Example Valid Data

• What lines of code indicates what is valid data?
• int x
• int y
• scanf("d d\n", x, y)
• Valid data is any integer. Positive, negative,
  or zero.

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Test data for all logical paths

• int x,y
• scanf("d d", x, y)
• if (x gt 2)
• while (x gt y)
• printf("S1,")
• x--
• printf("S2,")
• else if (x lt y)
• printf("S3,")
• printf("S4")

• What is done for every input?

• What does this say about the output?
• S4 must be output at the end every time.

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Test data for all logical paths

• int x,y
• scanf("d d", x, y)
• if (x gt 2)
• while (x gt y)
• printf("S1,")
• x--
• printf("S2,")
• else if (x lt y)
• printf("S3,")
• printf("S4")

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Test data for all logical paths
TO DO Test all paths from Input to Output S4
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Choice Points
Input x,y
xgt2?
NO
NO
xlty
xgty?
Paths are determined by choice points.
YES
YES
output S3
output S1
output S2
decrement x
output S4
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Choice Points

• int x,y
• scanf("d d", x, y)
• if (x gt 2)
• while (x gt y)
• printf("S1,")
• x--
• printf("S2,")
• else if (x lt y)
• printf("S3,")
• printf("S4")

• What are the highest level choice points?

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Choice Points
Input x,y

• What are the highest level choice points?

xgt2?
NO
NO
xlty
xgty?
YES
YES
output S3
output S1
output S2
decrement x
output S4
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Choice Points
Input x,y
Test data Case 1 NOT (xgt2), NOT (xlty)
xgt2?
Specific Values x2, y 2
NO
NO
xlty
xgty?
Output S4
YES
YES
output S3
output S1
output S2
decrement x
output S4
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Choice Points
Input x,y
Test data Case 2 NOT (xgt2), xlty
xgt2?
Specific Values x2, y 3
NO
NO
xlty
xgty?
Output S3, S4
YES
YES
output S3
output S1
output S2
decrement x
output S4
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Choice Points
Input x,y

• int x,y
• scanf("d d", x, y)
• if (x gt 2)
• while (x gt y)
• printf("S1,")
• x--
• printf("S2,")
• else if (x lt y)
• printf("S3,")
• printf("S4")

xgt2?
NO
NO
xlty
xgty?
YES
YES
output S3
output S1
output S2
decrement x
output S4
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Choice Points
Input x,y
Test data Case 3 (Loop body not executed) x gt
2, NOT(x gt y)
xgt2?
NO
NO
xlty
xgty?
Specific Values x3, y 4
YES
YES
Output S2, S4
output S3
output S1
output S2
decrement x
output S4
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Choice Points
Input x,y
Test data Case 4 (Loop body executed) x gt 2, x
gt y
xgt2?
NO
NO
xlty
xgty?
YES
Specific Values x5, y 4
YES
output S3
output S1
Output S1, S2, S4
output S2
decrement x
output S4
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Notes on Loop Tests

• Is it possible that the loop never terminates?
• only if algorithm is incorrect
• Example
• x gt y, AND decrementing x each step.

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Example Change in Algorithm

• Provide a set of test data
• valid
• valid boundary
• invalid

/ Step 1 / while (x gt 0) / Step 2 /
if (y 2) / Step 2a /
else / Step 2b / / Step 3
/ / Step 4 /

• How would you ensure that the loop will always
  terminate?

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Summary

• Testing is an important part of the software
  development process.
• Considering all the test data cases can lead to
  change in the algorithm.
• Flow Diagrams can be used to design the test data
  set.