Testing Input Fields with Boundary Value Technique

1
Testing Input Fields with Boundary Value
Technique
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Boundary Value Testing

• A type of Black box functional testing
• The program takes inputs and maps some out-puts
• The internal of the program itself is not
  considered
• A technique to generate test cases via
  considering (mostly) the inputs to the program
• The rationale for this focus is that there are
  experiences from the past which indicate that
  errors tend occur at the extreme points.
• Input data (legal versus illegal)
• Loop iteration (beginning and ending of loops)
• Output fields (legal versus illegal)

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A simple example

• Consider a program that reads the age of each
  person here and computes the average age of the
  people.
• input (s) ? Program ? output average age
• How would you test this?
• How many test cases would you generate?
• What type of test data would you input to test
  this program?

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Input (s) to Program Average

• First question would be - - - how many input
  data?
• The answer is some number 1 or more --- not too
  sure, yet.
• Second question would be --- what value should
  each input age be?
• Try some typical age such as 23 or 45
• Try some atypical age 125 or 700
• How about trying a wrong age of -5 or 0 or _at_
• When we try the atypical age or some wrong age,
  we may discover that the program may not handle
  or process properly ---- possibly resulting in a
  failure. Failure in this case, may include
  strange answer, but not necessarily program
  termination.

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Example Program Age Average

• Inputs composed of only typical ages 23, 67, 97
• Look at the output average, and the average is
  computed either
• Correctly
• Incorrectly
• Inputs composed of atypical or wrong ages
• What is an atypical or wrong age?
• Let us cap the age from 1 to 150.
• So the lower and upper boundaries for age is 1
  and 150, respectively.

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Boundaries of the inputs
1 lt age lt 150
150
age
1
The basic boundary value testing would include
5 situations 1. - at minimum
boundary 2. - immediately above minimum
3. - between minimum and maximum (nominal)
4. - immediately below maximum 5. - at
maximum boundary
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The Test Cases for this Example

• Howe many test cases for this example ?
• answer for this one field 5
• What types of test input values?
• 1 at the minimum
• 2 at one above minimum
• 45 at middle
• 149 at one below maximum
• 150 at maximum

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Single fault or independent faults

• For the previous problem, there was 1 input
  field. Suppose there are 2 distinct inputs that
  are assumed to be independent (single fault) of
  each other.
• Input field 1 years of education ( say 1 to 23
  )
• Input field 2 age
• If they are independent of each other, then we
  can start with looking at 5 5 10 sets, but
  wont need all 10 of them.

• coverage of input data yrs of ed
• 1. n 1 age whatever(37)
• n 2 age whatever
• 3. n 12 age whatever
• n 22 age whatever
• n 23 age whatever

• coverage of input data age
• 1. n 12 age 1
• n 12 age 2
• 3. n 12 age 37
• n 12 age 149
• n 12 age 150

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2 independent inputs
age
yrs of ed.
- Note that there needs to be only 9 test cases
for 2 independent variables or inputs. - In
general, there will be (4z 1) test cases for z
independent inputs.
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Some Limitations of Boundary Value Testing

• What would we do with boolean variables?
• True
• False
• (these may not be input fields but radio buttons)
• What about non-numerical variable where the
  values may be text?

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Robustness testing

• This is just an extension of the Boundary Values
  to include
• Less than minimum
• Greater than maximum
• There are 7 cases or values to worry about for
  each independent variable input.
• The testing of robustness is really a test of
  error handling.
• Do we anticipate the error situations?
• Do we issue informative error messages?
• Do we allow some kind of recovery from the error?

Levels of Problem Severity?
12
2 independent inputs for robustness test
X
Y
- Note that there needs to be only 13 test cases
for 2 independent variables or inputs. - In
general, there will be (6n 1) test cases for n
independent inputs.
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More on Robustness Testing

• Perhaps a little more than 7 test cases?
• beyond the boundary cases should include other
  illegal inputs
• For numeric field should we try some non-numeric
  input?
• How about blank or no input?
• So perhaps we ought to consider 8 or 9 as a more
  reasonable number of test cases when we consider
  all types of outside the boundary cases for
  Robustness Testing

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Worst-Case testing for non-independent variables

• If the input variables are not independent, then
  we would need to test all possible combinations
  of values that the variable may take on.
• For Boundary Value Testing, each of the 5
  possible values of a variable must iterate
  through the 5 possible values of the other
  variable(s).
• Thus for n input variables, there are 5n possible
  test cases
• For Robustness Testing, each of the 7 possible
  values of a variable must iterate through the 7
  possible values of the other variable(s).
• Thus for n input variables, there are 7n possible
  test cases

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2 non-independent inputs for worst case test
X
For 2 non-independent variables, there are 52
25 test cases
Y
- In general, there will be 5n test cases for n
non-independent inputs.
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Hierarchy

• For n number of variables (input fields)
• Boundary Value testing of n inputs 4n 1
• Robustness testing of n inputs 6n 1
• Worst case for boundary value 5n
• Worst case for robustness 7n

• Boundary Value is a subset of Robustness
• Worst case for boundary value is a subset of
  worst case of robustness

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Some Special Value and Random Testing

• Special Value Testing
• Based on experience
• Based on special knowledge of the industry
• Ad hoc in nature
• Has had some very valuable inputs
• Costly to find the industry experts
• Random Value Testing
• Based on some random number generator
• Generate values within bounds of the boundary or
  worst case
• The value of random test has not been clearly
  justified except we may be able to automate this

Especially for multiple dependent and legitimate
test cases