Modal Testing Strategies for Object Oriented Software

1
Modal Testing Strategies for Object Oriented
Software

2
Target

• To design a practical suite that exercises enough
  combination of message sequence and state
  interactions to provide sufficient confidence
• Challenges
• Interactions are often subtle
• Complex --gt Error Prone
• If classes were alike , it might be enough to
  devise tests based either on message sequence or
  state.
• Characterization of Class behavior difference to
  indicate appropriate test strategy ? Class
  Modality

3
Class Modality

• Characterization of Class behavior difference to
  indicate appropriate test strategy
• Class behavior is an abstraction of the response
  that objects can make to messages.
• A Response is determined by the content of the
  object or the message , the prior sequences of
  messages accepted , or both.
• Class Modality is a general pattern of behavior.
• Modality is determined by the class constraints
  on message sequence and instance variable content

4
Modalities for Testing

• A nonmodal class imposes no constraints on the
  sequences of messages accepted.
• Classes that implement relatively simple data
  types are often nonmodal.
• A unimodal class imposes constraints on message
  sequence, regardless of content.
• Classes that implement application control are
  typically unimodal.
• A quasimodal class imposes no constraints on
  message sequence, unless a domain constraint
  does.
• Many container and collection classes are
  quasimodal.
• A modal class has both message and domain
  constraints on message sequence.
• Classes that represents problem domain entities
  are often modal.

5
NonModal Class

• Consider a class names DateTime
• It encapsulates a representation of a single date
  and time and provides operation on this
  representation.
• This class imposes no constraints on the sequence
  of messages accepted . For example
• An object of DateTime class will accept any
  interleaving of set, get, compareEqual , GetGMT,
  and so on .

6

• To test this class we define the boundaries of
  the its instance variables.
• Second 0,59 Minute 0,59 Hour 0,23
• Day 0, 366 Year 1900, 65363 Zone 1, 24
  
• Table 1 shows how domain constraints are used
  with this pattern to generate test points, E
  indicates the Min val, II indicates Max valand
  set of points.

7
UniModal Class

• Consider class TrafficLight which implements a
  sequential control strategy for a traffic light.
• Working
• This class accepts messages that turn on one of
  three lights, but only if the request complies
  with the allowed sequence. If the message is sent
  out of order , the class raises an exception and
  does not change over.
• This class is Unimodal as an object of
  TrafficLight class can accept the message
  RedLightOn only after accepting a
  YellowLightOn message.

8
Testing

• Test Plan for TrafficLight has two parts.
• Conformance Test
• Sneak Path Test
• Conformance test are identified by tracing a
  transition tree from the state model.
• Each root-to-leaf branch is a test case
  consisting of a legal sequences of messages.
• The state obtained after this sequence must
  conform the state specified.
• However conformance alone is not sufficient as we
  must ensure that that incorrect sequences are
  rejected by an apprpriate response without
  corrupting state.
• Sneak Path Testing attempts every illegal message
  in every state.

9
The table shows the conformance and sneak Path
test suite.

10
QuasiModal Class

• Class Stack bases its response to a message on
  the content of a stack object, not on the last
  message sent.
• A quasimodal class imposes no constraint on
  message sequence. For example
• An object of class Stack will reject a push
  message if a stack is full but accept it
  ohterwise.
• The behavior of a quasimodal class is a result of
  properties and relationships that are independent
  of content ( a full stack if full, regardless of
  the values of the entries that have made it
  full).

11

• To test stack , we must test each variation of
  sequential constraints caused by variations in
  its domain.
• The test strategy has three steps
• Characterize states by constraints ( not by
  content)
• Apply the vertex probe strategy to the
  parameters.
• Identify specific values that will result in the
  sequences being exercised.

12
(No Transcript)
13
Modal Class

• Consider the class Account which is modal as it
  constraints both sequence and contents.
• Test strategy is Hybrid
• An N test plan is prepared , providing
  transition and sneak path test coverage,
• Vertex probe analysis is prepared.
• Test cases are added if any vertex probe points
  have not been reached by N cover.

14
Summary

• Each class modality is subject to different kinds
  of faults ? needs a different test strategy.
• Established domain testing strategies can be
  applied to classes and objects an integral
  wholes.
• Test points can be interleaved in a sequence that
  will also validate control implementation.
• Test suites that provide N and vertex coverage
  can be produced by analysis.