How to Fix “No Possible Values” Faster
Learn a strategy for identifying the cause of “no possible value” appearing in your tests and for fixing the corresponding constraint conflict.
Note: this document covers the NPVs caused by the flaws in user logic. Other scenarios, like 3-way constraints, could cause the NPVs that can most commonly be corrected manually after export.
The model used in this example has the following structure:
Intuitively, a test designer proceeds with the current model and applies the constraints in the following way:
One of the solutions, especially useful on larger models, involves 3 steps.
Step 1: Go to “Scenarios” tab in the ribbon and find the last row where “no possible value” appears (can use DesignWise search field/ Ctrl+F on Windows/ Command+F on Mac)
Because of this, the NPV in any row can only be caused by the parameter values in normal black font. At the bottom of the set, there is the minimum amount of such values; in this example, “I” and “9”.
Step 2: Now that we know the “guilty” values, go back to the Constraints tab and check all the relationships associated with both (refer to the list above).
Now, for Parameter 4 = I, there is no flexibility: as you can see from the list on the left, when “I” is chosen, Parameter 5 is always “3”, i.e. can’t be “9”.
This logical conflict creates the NPV – DesignWise can not select the pair of values which satisfies contradicting conditions.
Step 3: Once the problem is identified, find the right solution.
The specific correction depends on the model and business logic. In this case, the value “unassigned” should be added to Parameter 4 and matched (constrained against) Parameter 5=7 and Parameter 5=9.