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How do I write test cases for an application which consists of complex mathematical formula?

For example, suppose a user wants to calculate total cost and values coming from more than 3 or 4 modules/forms along with a condition. What will be the best approach for such a situation?

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Since you are dealing with complex calculations across multiple modules, your first priority is to test that the calculations of each module are correct. Only then can you properly handle testing across modules.

Let's say your app has 5 modules. Each module can interact with any of the others. We'll call them A, B, C, D, and E

The app also uses two different conditions. Call them x and y. To make things more interesting, let's say that x applies to A, B, and C; and y applies to C, D, and E.

Now let's look at your potential test scenarios - you will of course start with testing each module in isolation and checking that the calculations are accurate. For each module, you should use a range of inputs the more or less follow this pattern:

  • Invalid input below the minimum allowed value
  • Exactly the minimum allowed value
  • Somewhere in the allowed range
  • Exactly the maximum allowed value
  • Invalid input above the maximum allowed value

Since this set of tests also covers testing without condition x or y, your next set of tests applies the appropriate condition, and checks that you can't apply condition x to modules D & E, and that you can't apply condition y to modules A & B. You would also need to make sure that module C calculations work correctly when both condition x and y are applied.

At this point, you know that each module behaves correctly with and without conditions applied.

After that, it's simply a matter of working out what the output should be for whichever combination you're using, and checking that the application returns the correct output. Ideally there would be automated testing to tell you that the modules are behaving correctly, but if not, you would need to handle the testing of those before starting your more complex test.

That's really all that's involved. Cover each component in isolation, then in combination. I personally would start the combination tests with two components in combination, then move to 3 and so on. I would also, as much as time permits, change only one thing in each new test. So when testing say modules A & B, I'd test:

  • A without condition x, B without condition x
  • A with x, B without x
  • A with x, B with x
  • A without x, B with x

And so on.

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There are many situations where the product in a software qa company is having complex calculation with the dependency on other modules. Below would be an example for you:

There is product that calculates "Member's Appraisal". Below are the dependent criteria's: - Performance rating coming from Module A - Current Salary coming from Module B - Year of Experience coming from Module C.

So to make the the test case to check we can write in this way:

Summary: Correct Appraisal should be calculated in the generated annexure.

Pre-requisite:
1. Members Performance Rating should be available in Module A.
2. Members Current Salary should be available in Module B.
3. Members Year of Experience should be available in Module C.

Steps to execute:
1. Login to "Member's Appraisal" application.
2. Observe the data for the Member is getting populated from Module A, Module B and Module C.
3. Provide the Appraisal % age and observe.

Expected result: Correct Appraisal should be calculated in the generated annexure.

So here the tester will confirm that the correct data is getting picked from Module A,B and C.

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