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Quality Engineering >> Requirements and Design

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sudhi_silk
Newbie


Reged: 06/17/09
Posts: 18
Enough test cases to cover a specific requirement
      #707607 - 05/21/12 07:15 PM

Hello,

Suppose I have a single line functional requirement for a product, how many test cases should I be writing to say that requirement is thoroughly tested.

Example: I have the following requirement

User needs to sign up to create his email id and this needs to be authorized by a Ops manager, so that user can start accessing his email account.

My Question:

How many test cases I need to write to make sure that all the aspects of the requirements are covered ?

Suppose one tester can write 5 test cases, another can write 20 test cases and yet another can write 50 testcases.

So the point is how can I justify that x number of test cases are sufficient for the given requirement.

Thanks
Sudhi

Edited by sudhi_silk (05/21/12 09:46 PM)


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Richard_Hunter
Member


Reged: 08/16/04
Posts: 388
Re: Enough test cases to cover a specific requirement [Re: sudhi_silk]
      #707629 - 05/22/12 01:30 AM

This is alway a "depends" answer. Depends on what you are trying to acheive to how much testing you are going to do.

I think this is down to assessing risk, and then deciding on coverage.

I would always advise for every requirement assessing the risk with the business (how important is it, how often is it used) and the technical risk (how hard is it) and scoring each requirement.

You then have a list of how important each requirement is to test.

Then for each requirement you need to assess what test techniques are appriopriate and what test phase you are going to test it in. This provides the coverage matrix. (remember testing starts at unit testing)

You can then come up with the logical test cases for each requirement, in each test phase, based on the techniques decided upon above. Then you can create a physical test cases to incorporate the logical test cases. (Plug alert, TMap Next describes this in great detail http://www.tmap.net/en/tmap/).

In other words, work out what you are trying to prevent, so you can work out the level, types and coverage of testing you need.

Taking your example 'User needs to sign up to create his email id and this needs to be authorized by a Ops manager, so that user can start accessing his email account.'

(All score High (5 points), Medium (3 points), Low (1 point))

Business question - how often is this used?
Business answer - 5-10 people a year.
Score - Low(1)

Business question - what is the impact of a failure?
Business answer - Large reputational damage
Score - High(5)

Total Business Score = 6

Technical Question - how often is the code used by other parts (is it a shared component)
Technical Answer - only used by this functionality
Score - Low (1)

Technical Question - How complex is this?
Technical Answer - Hard, this is integrating to a third party that we have not done before.
Score - High (5)

Total Technical Score = 6

Total Score = 12

Then repeat for all requirements. Anything that is a score 16-20 is the highest band, 12-14 Band B, 8-10 Band C, 4-6 Band D. This allows you to focus more testing on Band A etc

I will not keep on going with this, but you then decide how you are going to test each requirement at each level of testing to provide sensible coverage based on the priority.

(Note - the priority can change throughout, especially on something that appeared to be easy has lots of defects in, you might want to revisit how you are testing it)


Edited by Richard_Hunter (05/22/12 01:32 AM)


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mbalajiwale
Member


Reged: 07/29/11
Posts: 60
Re: Enough test cases to cover a specific requirement [Re: Richard_Hunter]
      #707630 - 05/22/12 01:37 AM

Motive while writing test cases should be the complete and correct coverage of requirement. Nothing should be missed. In order to achieve that if you feel to add 5 or 50 test cases does not matter. But it is a good practice to write a separate test case for each functionality. And if required it can further be divided in 'n' number of steps to break it down to lower level. Like to login, you first need to connect to the URL then enter user name and password then click on 'Submit'/'Ok' etc button. This can be written in single test case or can be divided in 3 steps under single test case.

In short number of test cases can't assure requirement coverage, it is the content of test case which should cover all aspects of a requirement.

Hope this would be useful to you. Get back to me with your thoughts on the same.

Thanks.

--------------------
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mbalajiwale


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Richard_Hunter
Member


Reged: 08/16/04
Posts: 388
Re: Enough test cases to cover a specific requirement [Re: mbalajiwale]
      #707635 - 05/22/12 01:47 AM

mbalajiwale - complete coverage for every requirement? Are you sure? What do you mean by complete? I have seen many requirements that would have me testing to the end of my days to get complete coverage.

--------------------
Richard Hunter


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mbalajiwale
Member


Reged: 07/29/11
Posts: 60
Re: Enough test cases to cover a specific requirement [Re: Richard_Hunter]
      #707638 - 05/22/12 02:02 AM

yes agree...no limit to write details in a test case. For that we need to understand what exactly end user needs from this functionality, how end user would make use of this functionality and draw a line to the detailing. Practice which we would follow is once requirements are given, go through those, understand those and share understanding with BA's, end users, get confirmation and write test cases. Else there is not end to have complete coverage for a test case.

Please share your thoughts on the same, that will definitely enhance my knowledge

Thanks.

--------------------
_____________________
Regards,
mbalajiwale


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Joe Strazzere
Moderator


Reged: 05/15/00
Posts: 12344
Loc: Massachusetts, USA
Re: Enough test cases to cover a specific requirement [Re: sudhi_silk]
      #707648 - 05/22/12 03:55 AM

Quote:

So the point is how can I justify that x number of test cases are sufficient for the given requirement.



You can't. There aren't any magic numbers in the software testing business.

There is no number X, such that X test cases must always be written for any requirement. Each requirement is different, and may demand a different number of test cases to feel comfortable that it is adequately covered to the extent you need it covered.

The only way to ensure sufficiency is for you to understand the requirements and the test cases themselves and then analyze them individually.

No magic formula. No shortcuts. Just work.

--------------------
- Joe
Visit AllThingsQuality.com to learn more about quality, testing, and QA!

I speak only for me. I do not speak for my employer, nor for anyone else.


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Joe Strazzere
Moderator


Reged: 05/15/00
Posts: 12344
Loc: Massachusetts, USA
Re: Enough test cases to cover a specific requirement [Re: sudhi_silk]
      #707651 - 05/22/12 03:58 AM

Quote:

Example: I have the following requirement

User needs to sign up to create his email id and this needs to be authorized by a Ops manager, so that user can start accessing his email account.

My Question:

How many test cases I need to write to make sure that all the aspects of the requirements are covered ?



I could write 1 large test case, or 500 smaller test cases.

But based solely on the numbers 1 or 500, you still cannot have any confidence that all the requirements are covered unless you are willing to dig in and understand both the requirements and the test cases.

--------------------
- Joe
Visit AllThingsQuality.com to learn more about quality, testing, and QA!

I speak only for me. I do not speak for my employer, nor for anyone else.


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munagaraja
Newbie


Reged: 06/17/08
Posts: 8
Loc: Bangalore
Re: Enough test cases to cover a specific requirement [Re: Joe Strazzere]
      #710957 - 06/28/12 12:59 AM

The question always we should be asking ourselves is how to cover the given requirement effectively rather than how many test cases will cover the requirement. We can never say that X number of test cases will cover the requirement. There is no FIXED number we can arrive at to say that a requirement is completely covered. The idea behind writing test cases is to make sure the software works the way business requirement is given and there are no bugs in the code.

--------------------
Thanks,
Nagaraj
--------------------------------------------
"You're never a loser until you quit trying." Ditka, Mike


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Christian Grzelka
Active Member


Reged: 02/02/05
Posts: 740
Loc: Bordeaux, France
Re: Enough test cases to cover a specific requirement [Re: munagaraja]
      #711010 - 06/28/12 08:34 AM

Maybe, we can give a number if, instead of test cases, we look at use cases.

You do not (or should not) define your test cases on this kind of requirements : developers should build a solution for it ; part of that build can (should ?) be a list of use cases ; your test cases are to be designed against the user cases ; not the user requirement...

And your first test case would be to verify that the use cases designed by the developers fulfill the requirement.


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