What does No possible value means?

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Hi, may i ask what does "No possible value" means in the output of 2-way generated tests?

Thank you!

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Helen Noynay

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  • confused

Posted 8 years ago

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Sean Johnson, CTO

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Official Response

Sure! I assume you have some invalid pairs in this test plan? What the "no possible value" is trying to tell you is that the test case is providing coverage for a needed pair, and that the way you have your invalid pairs setup then prevents this test from being able to provide a value for that parameter in light of that needed pair and the invalid pairs. That sounds confusing, I know, so an example is much easier to understand.

Let's say we have a test plan with 3 parameters, each with 2 values:

Fruit: Apple, Pear
Car: Toyota, Dodge
Dog: Collie, Mutt

And let's further suppose we have 2 invalid pairs:

if Fruit = Apple then Car != Toyota
if Car = Dodge then Dog != Mutt

To create 2-way coverage, Hexawise will ensure you've paired every parameter value with every other parameter value (unless an invalid pair says it shouldn't be paired), which in this case means that Hexawise will necessarily pair Fruit as Apple with Dog as Mutt in at least one test case, since that pairing could be the source of a bug. You probably already see the problem!

In the test case that has Fruit as Apple and Dog as Mutt we need to have a test value for the Car parameter. You can't have Car as Toyota, because Apple can't be paired with Toyota, and you can't have Car as Dodge, because Mutt can't be paired with Dodge. So what value can Hexawise provide for Car in this test case? It has no value to provide, there is none, so it provides "no possible value".

That's why you get these cases. Generally, given the real context of your actual test plan, it is clear what to do to resolve these. Sometimes your invalid pairs may need a bit of adjusting, sometimes you might want to introduce a "N/A" value for a parameter, etc.

If you have a real-life case where it's not so clear what to do, let us know and one of us would be more than happy to hop on the phone and talk through that test plan with you.