unit 7 testing

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UNIT 7

STATES,STATE GRAPHS AND

TRANSITION TESTING

D.ABHISHEKH MS(SE)

State Graphs

A state is defined as : A combination of circumstances or attributes belonging for the time being to a person or thing.

For example, a moving automobile whose engine is running can have the following states with respect to its transmission.

Reverse gear

Neutral gear

First gear

Second gear

Third gear

Fourth gear

State graph - Example

For example, a program that detects the character sequence ZCZC can be in the following states.

Neither ZCZC nor any part of it has been detected.

Z has been detected.

ZC has been detected.

ZCZ has been detected.

ZCZC has been detected.

None Z ZC ZCZ ZCZC

Z C Z C

Z

A,C Z,C,A

Z

A

AA,C

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STATE OKAY

ERROR

1 1/NONE 2/REWRITE

2 1/NONE 4/REWRITE

3 1/NONE 2/REWRITE

4 3/NONE 5/ERASE

5 1/NONE 6/ERASE

6 1/NONE 7/OUT

7

TRANSITION BUGS

Example to convert specification into a state graph

----------------------------------------------------------------

With an example, we will now follow a set of rules, i.e. specifications to deduce the state graph and state tables

RULE 1:

The program will maintain an error counter which will be incremented

whenever there is an error.

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Initial state graph deduced from Rule1

error error error error . . .

Okay

RULE 1: The program will maintain an error counter,

which will be incremented whenever there is an

error.

0 1 2 3 4

State table from the state graph(refer earlier slide for the

graph)

STATE OKAY ERROR

0 0/None 1/

1 2/

2 3/

3 4/

4 5/

5 6/

6 7/

7 8/

INPUT

Rule 2: If there is an error, rewrite the block

STATE OKAY ERROR

0 0/None 1/REWRITE

1 2/REWRITE

2 3/REWRITE

3 4/REWRITE

4 5/REWRITE

5 6/REWRITE

6 7/REWRITE

7 8/REWRITE

INPUT

For all Error entries, we include a Rewrite

Rule 3: If there have been 3 successive errors, erase of tape and then rewrite the block

STATE OKAY ERROR

0 0/None 1/REWRITE

1 2/REWRITE

2 3/REWRITE,ERASE,REWRITE






INPUT

The first 3rd successive error

occurs

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STATE OKAY ERROR

0 0/None 1/REWRITE

1 2/REWRITE

2 3/REWRITE,ERASE,REWRI

TE


TE


TE

5 6/OUT

6

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Rule 4: If there have been 3 successive erasures, and another error occurs, put the unit out of service

We have 3 successive erasures- so

we now put the unit out of service

Rule 5: If the erasure was successful, return to the

normal state and clear the error counter

STATE OKAY ERROR

0 0/None 1/REWRITE

1 2/REWRITE


TE

3 0/None 4/REWRITE,ERASE,REWRI

TE


TE

5 0/None 6/OUT

6

7

We reach State 3 after the 1st

erasure. If successful, we return to

None & the error counter is made

0

Rule 6: If the rewrite was successful, decrement the

error counter and return to the previous state

STATE OKAY ERROR

0 0/None 1/REWRITE

1 0/None 2/REWRITE


TE

3 0/None

2/None

4/REWRITE,ERASE,REWRI

TE

4 0/None

3/None

5/REWRITE,ERASE,REWRI

TE

5 0/None

4/None

6/OUT

6

7

INPUT

Example: Say we are at state 1. The error

counter here is 2. If we have a

successful(okay) rewrite, the entry for okay

at state 2 will have error counter

decremented by 1 which is:

(2-1)/None where, None output for success.

Conclusion

Observe the previous slide-RULE6 states If the rewrite was successful, then decrement the error counter and return to the previous state. The requirement probably was If there have been no erasures and rewrite was successful, then

This has now resulted in contradictions which is a concern as it might lead to bugs.

It is always unlikely that a contradictory specification can result in a satisfactory implementation.

unit 7 testing

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