SE 4367 Functional Testing

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SE 4367Functional Testing
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Learning Objectives

• What is functional testing?

• How to perform functional testing?

• How to generate test inputs?

• What are equivalence partitioning, boundary value
  testing, domain testing, state testing, and
  decision table testing?

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What is Functional Testing?

• When test inputs are generated using functional
  specifications, we say that we are doing
  functional testing.

• Functional testing tests how well a program meets
  the functionality requirements.

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The Methodology

• The derivation of test inputs is based on
  functional specifications.

• Clues are obtained from the specifications.

• Clues lead to test requirements.

• Test requirements lead to test specifications.

• Test specifications are then used to actually
  execute the program under test.

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Test Methodology
Specifications
Program output is correct
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Equivalence Partitioning

• The input domain is usually too large for
  exhaustive testing.

• It is therefore partitioned into a finite number
  of sub-domains for the selection of test inputs.

• Each sub-domain is known as an equivalence class
  and serves as a source of at least one test
  input.

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Equivalence Partitioning
Four test inputs, one selected from each
sub-domain.
Too many test inputs.
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How to partition?

• Inputs to a program provide clues to partitioning.

• Example 1
• Suppose that program P takes an integer X as
  input X.
• For XT1 and for X0 task T2.

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How to partition? (contd.)

• The input domain is prohibitively large because X
  can assume a large number of values.

• However, we expect P to behave the same way for
  all X

• Similarly, we expect P to perform the same way
  for all values of X0.

• We therefore partition the input domain of P into
  two sub-domains.

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Two sub-domains
All test inputs in the Xconsidered equivalent. The assumption is that if
one test input in this sub-domain reveals an
error in the program, so will the others. This
is true of the test inputs in the X0 sub-domain
also.
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Non-overlapping Partitions

• In the previous example, the two equivalence
  classes are non-overlapping. In other words the
  two sub-domains are disjoint.

• When the sub-domains are disjoint, it is
  sufficient to pick one test input from each
  equivalence class to test the program.

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Non-overlapping Partitions

• An equivalence class is considered covered when
  at least one test has been selected from it.

• In partition testing our goal is to cover all
  equivalence classes.

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Overlapping Partitions

• Example 2
• Suppose that program P takes three integers X, Y
  and Z. It is known that
• X
• ZY

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Overlapping partitions
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Overlapping Partition-Test Selection

• In this example, we could select 4 test cases as
• X4, Y7, Z1 satisfies X
• X4, Y2, Z1 satisfies XY
• X1, Y7, Z9 satisfies ZY
• X1, Y7, Z2 satisfies Z

• Thus, we have one test case from each equivalence
  class.

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Overlapping Partitions-Test Selection

• However, we may also select only 2 test inputs
  and satisfy all four equivalence classes
• X4, Y7, Z1 satisfies X
• X4, Y2, Z3 satisfies XY and ZY

• Thus, we have reduced the number of test cases
  from 4 to 2 while covering each equivalence class.

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Partitioning using non-numeric data

• In the previous two examples the inputs were
  integers. One can derive equivalence classes for
  other types of data also.

• Example 3
• Suppose that program P takes one character X and
  one string Y as inputs. P performs task T1 for
  all lower case characters and T2 for upper case
  characters. Also, it performs task T3 for the
  null string and T4 for all other strings.

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Partitioning using non-numeric data
lc Lower case character UC Upper case
character null null string.
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Non-numeric Data

• Once again we have overlapping partitions.

• We can select only 2 test inputs to cover all
  four equivalence classes. These are
• X lower case, Y null string
• X upper case, Y not a null string

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Guidelines for equivalence partitioning

• Input condition specifies a range create one for
  the valid case and two for the invalid cases.

• e.g. for a
• a
• Xb (the invalid cases)

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Guidelines (contd.)

• Input condition specifies a value create one for
  the valid value and two for incorrect values
  (below and above the valid value). This may not
  be possible for certain data types, e.g. for
  boolean.

• Input condition specifies a member of a set
  create one for the valid value and one for the
  invalid (not in the set) value.

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Sufficiency of Partitions

• In the previous examples we derived equivalence
  classes based on the conditions satisfied by the
  input data.

• Then we selected just enough tests to cover each
  partition.

• Think of the advantages and disadvantages of this
  approach!

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Boundary Value Analysis (BVA)

• Another way to generate test cases is to look for
  boundary values.

• Suppose a program takes an integer X as input.

• In the absence of any information, we assume that
  X0 is a boundary. Inputs to the program might
  lie on the boundary or on either side of the
  boundary.

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BVA (contd.)

• This leads to 3 test inputs
• X0, X-20, and X14.

Note that the values -20 and 14 are on either
side of the boundary and are chosen arbitrarily.

• Notice that using BVA we get 3 equivalence
  classes. One of these three classes contains only
  one value (X0), the other two are large!

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BVA (contd.)

• Now suppose that a program takes two integers X
  and Y and that x1

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BVA (contd.)

• In this case the four sides of the rectangle
  represent the boundary.

• The heuristic for test selection in this case is
• Select one test at each corner (1, 2, 3, 4).
• Select one test just outside of each of the four
  sides of the boundary (5, 6, 7, 8)

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BVA (contd.)

• Select one test just inside of each of the four
  sides of the boundary (10, 11, 12, 13).

• Select one test case inside of the bounded region
  (9).

• Select one test case outside of the bounded
  region (14).

• How many equivalence classes do we get?

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BVA (contd.)

• In the previous examples we considered only
  numeric data.

• BVA can be done on any type of data.

• For example, suppose that a program takes a
  string S and an integer X as inputs. The
  constraints on inputs are
• length(S)

• Can you derive the test cases using BVA?

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BVA Applied to Output Variables

• Just as we applied BVA to input data, we can
  apply it to output data.

• Doing so gives us equivalence classes for the
  output domain.

• We then try to find test inputs that will cover
  each output equivalence class.

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Finite State Machines (FSMs)

• A state machine is an abstract representation of
  actions taken by a program or anything else that
  functions!

• It is specified as a quintuple
• A a finite input alphabet
• Q a finite set of states
• q0 initial state which is a member of Q.

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FSMs (contd.)

• T state transitions which is a mapping
• Q x A-- Q
• F A finite set of final states, F is a subset of
  Q.

• Example Here is a finite state machine that
  recognizes integers ending with a carriage return
  character.

• A0,1,2,3,4,5,6,7,8,9, CR
• Qq0,q1,q2
• q0 initial state

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FSMs (contd.)

• T ((q0,d),q1),(q1,d),q1), (q1,CR),q2)
• F q2

• A state diagram is an easier to understand
  specification of a state machine. For the above
  machine, the state diagram appears on the next
  slide.

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State diagram
d denotes a digit
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State Diagram-Actions
x/y x is an element of the alphabet and y is an
action.
d/iid10j jj1
d/ i d j 1
CR/output i
i is initialized to d and j to 1 when the machine
moves from state q0 to q1. i is incremented by
10jd and j by 1 when the machine moves from q1
to q1. The current value of i is output when a CR
is encountered.
Can you describe what this machine computes?
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State Machine Languages

• Each state machine recognizes a language.

• The language recognized by a state machine is the
  set S of all strings such that
• when any string s in S is input to the state
  machine the machine goes through a sequence of
  transitions and ends up in the final state after
  having scanned all elements of s.

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State diagram-Errors
d/iid10j jj1
d/ i d j 1
CR/output I
CR/output error
reset
q4
q4 has been added to the set of states. It
represents an error state. Notice that reset is a
new member added to the alphabet.
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State Diagram-Code

• A state diagram can be transformed into a program
  using case analysis. Let us look at a C program
  fragment that embodies logic represented by the
  previous state diagram.

• There is one function for each action.

• digit is assumed to be provided by the lexical
  analyzer.

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Program for integer state machine
/ state is global, with values q0, q1, q2. i is
also global./
void event_digit()

• case q0
• idigit j 1 / perform action. /
• stateq1 / set next state. /
• break / event digit is done. /
• case q1
• ii10jdigit j / Add the next digit. /
• stateq1
• break
• /complete the program. /

switch (state)
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Checking State Diagrams

• Unreachable state One that cannot be reached
  from q0 using any sequence of transitions.

• Dead state One that cannot be left once it is
  reached.

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Test Requirements

• Every state must be reached at least once, Obtain
  100 state coverage.

• Every transition must be exercised at least once.
  Obtain 100 transition coverage.

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Example Test Requirements

• For the integer state machine
• state machine transitions
• event digit in state q0
• event CR in state q0
• event digit in state q1
• event CR in state q1
• event reset in state q4

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More testing of state machines?

• Yes, it is possible!

• When we learn about path coverage we will discuss
  how more test requirements can be derived from a
  state diagram.

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Test Specifications

• As before, test specifications are derived from
  test requirements.

• In the absence of dead states, all states and
  transitions might be reachable by one test.

• It is advisable not to test the entire machine
  with one test case.

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Decision Tables

• Requirements of certain programs are specified by
  decision tables.

• A decision table is useful when specifying
  complex decision logic

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Decision Tables

• A decision table has two parts
• condition part
• action part

• The two together specify under what condition
  will an action be performed.

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Decision Table-Nomenclature

• C denotes a condition
• A denotes an action
• Y denotes true
• Ndenotes false
• X denotes action to be taken.
• Blank in condition denotes dont care
• Blank in action denotes do not take the action

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Bank Example

• Consider a bank software responsible for debiting
  from an account. The relevant conditions and
  actions are
• C1 The account number is correct
• C2 The signature matches
• C3 There is enough money in the account
• A1 Give money
• A2 Give statement indicating insufficient funds
• A3 Call vigilance to check for fraud!

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Decision tables
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Example (contd.)

• A1 is to be performed when C1, C2, and C3 are
  true.

• A2 is to be performed when C1 and C2 are true and
  C3 is false.

• A3 is to be performed when C1 is true and C2 is
  false.

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Default Rules

• Are all possible combinations of conditions
  covered?

• No! Which ones are not covered?

• We need a default action for the uncovered
  combinations. A default action could be an error
  report or a reset.

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Example-Test Requirements

• Each column is a rule and corresponds to at
  least one test requirement.

• If there are n columns then there are at least n
  test requirements.

• What is the maximum number of test requirements?

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Example-Test Specifications

• For each test requirement find a set of input
  values of variables such that the selected rule
  is satisfied.

• When this test is input to the program the output
  must correspond to the action specified in the
  decision table.

• Should the testing depend on the order in which
  the conditions are evaluated?

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Summary-continued
Number of test cases
high
low
Sophistication
Boundary Value
Equivalence Class
Decision Table
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Summary-continued
Effort to Identify Test Cases
high
low
Sophistication
Boundary Value
Equivalence Class
Decision Table