State Transition - Switch Coverage Explained

State Transition

In this post, I would like to explain more about State transition Testing and 'N- Switch' Coverage. Let us consider sample question below and try to solve it.

Q: Given the following state transition

Which of the following series of state transitions below will provide 0-switch
coverage?

Answers:
i) A, B, E, B, C, F, D.
ii) A, B, E, B, C, F, F.
iii) A, B, E, B, C, D.
iv) A, B, C, F, F, D.

Before jumping on to solving this question, Lets get concept of N-switch in this particular example its 0-switch. What do you think is this 0- switch ?

If every valid transition is tested considering one transition at a time then, this is known as “0-switch” coverage. If you test a series of transitions through more than one state. If you covered all of the pairs of two valid transitions, you would have “1-switch” coverage, covering the sets of 3 transitions would give “2-switch” coverage, etc.

0- Switch Coverage

I tried to draw single transaction that is possible from each state in the above diagram So, going over this:

SS - S1 = A so, now you are in S1 state look for possible transactions from state S1

S1 - S2 = B we are at S2, looking at diagram you can see there are two possible transaction

S2 - S1 = E so now we are back at S1 and we know from S1 only possible transaction is to S2 

S1- S2 = B as we already covered S2 - S1 lets cover other possibility now

S2 - S3 = C

S3 - S3 = F

S3 - ES = D

Hence, Answer to above question is i)

Going beyond this question, let me ask question differently. How many test cases are needed to cover 0 - switch ? In this case it is 6 test cases.

1- Switch Coverage

Considering same example above, below sketch gives idea of how 1- switch Coverage

In order to have 1- Switch coverage of this state transition you need 7 Test cases.

• SS-S1-S2
• S1-S2-S3
• S1-S2-S1
• S2-S3-S3
• S2-S3-ES
• S2-S1-S2
• S3-S3-ES

I hope, with above examples its clear how 0 - Switch and 1- Switch or in general N- Switch coverage works. if in any case of any questions. Reach out to me :)