Use test-cases to validate your design with stakeholders

This post is part of a series about specifications, requirements, work items and test-cases in the field of Business Intelligence solutions. First part is about why I hate and I’d not recommend specifications, the second is about how to write good requirements for BI solutions. Then, in the third part I set the focus on work items and what does it mean according to me. I’ll now explain the role of test-cases in this strategy to deliver good BI solutions.

Let’s go back and see what is on the table until now:

  • Requirements:
    • A description of the business process to be analyzed
    • List of “what” (and not “how”) the stakeholders are expecting to do with our solution.
    • Information about the end-users (experience, …)
  • Work items
    • A general design, the solution that I’m planning to build
    • A list of deliverables to be implemented, each of them is a small and independent (meaning that they can be discarded or postponed).

Until now, we haven’t validated anything. General design and work items are just the team’s vision of what could be the best solution for the end-users. If we’re implementing this, we take a lot of risks. Too many! If something is not correctly described in the requirements or something not understood in the business process, we’ll only know it when revealing the solution to the end-users, it will be too late. We must have a hand shake between the implementation team and the stakeholders before implementing the whole solution, ideally before developing the first lines of code.


Keep in mind that you should never ask to the stakeholders to give a “go” for the whole solution. Will you ask them to confirm that the solution you’ve in your head is perfectly what they want with just a high level description (slides, whiteboard, …). It’d just be impossible (even for you). That’s the same than expecting from you to give a precise amount of hours to implement a solution with just a few lines of requirements.

We need to have a validation from stakeholders but what can we ask them to validate? Work items? The main issue with work items is the difficulty for end-users to have a good vision of what will be the solution: “What they will have in their hands”! Work items are usually too small to give them this overview. If we ask them to validate something else than the work items, we’ll also be responsible that work items and this “other thing” are related to each others during the whole implementation process.

So, the first option is to write a 3000 pages document with a really detailed explanation of what will be built. Cross your fingers that the stakeholders have time to read it (by experience, they won’t … and yes it will be your problem now or later but it will be). If they have time let me guess that won’t understand more than 50% (again sooner or later, it will be an issue for you).  Don’t forget to pray that you’ve not make some small mistakes in this description, or it will be your responsibility! You’ll need to deliver it (even if it’s not possible)… and don’t forget that this document must be written before the development so without any compiler to check your rough ideas. Oh, finally, you’ll need to maintain the link between this document and your work items. From my experience, go an buy a lottery ticket, you’ve more chances to succeed.


A second option? Write test-cases. Most of the industry practices ask stakeholders to validate “designs” or “specifications” but rarely “test-cases”. When you think about it, it’s weird: test-cases are much more precise and less abstract than the two others, so it’s easier to understand for the stakeholders and we’ve less opportunities to discuss the interpretation of a test-case than the interpretation of a specification. Funny. From my experience of the software industry, it’s usually because consultancy company don’t write test-cases … they are relying on end-users to effectively tests! And both (stakeholders and consultants) think that they are saving money with this “strategy”. Are we serious?


Let’s go back to test-cases. A common definition is “A test-case is a set of conditions under which we will determine whether an application, software system or one of its features is working as it was originally established for it to do”.

We can reverse the definition and say that “the way the application, software system or one of its features is expected to work is define by a set of conditions named a test-case”. It means that to express the result that I want (the what), I’m explaining what I’ll execute(the how). It gives a very good opportunity to keep the discussion with the stakeholders at the what-level and not the how-level. When you’re validating the test-case, you ask them to validate that it’s effectively the expected result … and not that it’s effectively how they were dreaming to implement it.

The difference between validating a “specification” and a “test-case” can be explained in a few words: Don’t ask them to validate a formulae, ask them to validate the output of the formulae when it receives a given set of parameters in input. That’s completely different.

Let me be clear on one important topic: validating a test-case has two points. The first is obvious, when you’re giving these parameters, you’re expecting this result. The second is less obvious ; you must also validate that the end-users are effectively able to give the parameters. For many reasons (usage of codes in place of labels, data not available at the moment of the request, …), the solution could not be implementable or usable!

How should you build the test-cases? From the end-user point of view: Show them the report or pivot table that are expecting/will receive. Don’t bother them with validation of the ETL … they don’t care and it’s not their problem, it’s yours. I agree that 50% of the errors will be in the ETL but it’s not something that you should discuss with end-users!Focus on deliverables: a dimension, a measure-group, a report and alert!


The big issue with BI solutions is usually that when we’re speaking about input parameters, we’re speaking a thousand or a million values. Building datasets for test-cases can be a huge task. My recommendation is to use real and already existing data as much as possible. If you can use production data (of the previous years). If you can’t argue for it and show to stakeholders the cost of building datasets … they could change their mind. If it’s really not possible, you’ll need to build datasets. But in both cases, really think about the need to assert the final result on all the data, a subset won’t be enough.

To illustrate this, I’ll explain my own case. At my current job, we’ve complex aggregations over time and the daylight savings switches are a nightmare for us. Some testers would try to validate all the aggregations at the day level for the 14 years of data. It will take them days to implement  … Who will validate such a result? do you really think that someone will spent his time to validate 5000 complex sums/averages/weighted averages? No one. I’m recommending to test one standard day and to test the two daylight savings of a same year. 3 tiny test-cases versus one huge test-cases.

There is another big advantage to use tiny test-cases versus huge test-cases. When my test will be successful for the standard day and the summer daylight saving but not for winter, I’d directly understand that I’ve a problem in loading my data for the winter shift and nowhere else. But when your huge case is failing, you must first analyze it deeply to check what is exactly failing and it could take a lot of time before realizing that it’s just for the winter shift that you’ve an issue.

But what will happens if my solution is correct for these 3 days but not for the others? I could have a bug that the solution is not loading the data before the year 2015! That’s a possibility and it’s why I should have some tiny tests with aggregation at the year level to ensure that I’m not only loading the last years of data. … but check my words … my test has changed! I’m not anymore testing that I’ve a correct aggregation, I’m testing that I’ve plausible values! Something that is usually much more quick to write and to validate.

The building of the set test-cases should be done with stakeholders. lets go back to an illustration from the real world. A few years ago, on of my testers spent many hours to implement a mock-up of a pivot table. The mock-up was with real figures and he spent a lot of times to calculate the expected content of each cell (around 16). After one day of work, he met the subject matter expert. In less than one second, the answer was there: “No, something is wrong!”. How could he says in less than 10 seconds that it was wrong. First, we had an issue with units (KW or MW), it means that all the figures had been a thousand times larger than expected. for him it was obvious, for us we had no idea if it was 45 or 45.000. In less than one second the subject-matter expert could identify that something was wrong but also explain how to fix it. Great! But there was something else, another issue. The expert started to move the members in a different sort and then identified another mistake some values were expected to be zero and it wasn’t. The expert explained that the lower part of the matrix should be zero due to the business process and it wasn’t the case. We discussed about the potential root causes of our mistakes and identified a wrong interpretation of a business rule described in the requirements. In just a few minutes we captured 3 potential mistakes in the development (units, sorting of members, business rule misinterpretation) … They continued to work together during one hour and reviewed the whole test-suite, adding test-cases that only subject matter experts could bring on the table and simplifying many test-cases. Great added-value for everyone.


At the opposite of writing work items, writing test-cases can be executed by juniors and seniors developers. What … developers writing tests? If your team members or you can’t write tests by themselves how could you hope that you develop with a minimum of bug? How can you anticipate all potential issues?  That’s the definition of testing. If a tester has absolutely no notion of development, I’ve huge doubt that he can anticipate potential issues, it’s just monkey testing. It has some value but does it sound serious to build your testing strategy on exclusively performing monkey testing? I doubt.

Nevertheless, if your team is totally new to testing, it could be useful to add a test manager to your team during a few months (or years). He should be able to review the test-cases with you, help you to identify alternative paths … help your team to go to the next level of maturity in testing. But your developers should write the test-cases by themselves. Not necessarily  write the test-cases on what they are implementing. They can pair with another implementer and one is testing the work-item that the other is coding (and vice versa).

Writing a test-case, is a slow (but valuable) process. I usually recommend a 1:1 ratio between the time of writing (not executing) the test-case and the time to develop the code. Keep in mind that I’m not just writing a test-case on a sheet of paper. I’m also validating my solution with the stakeholders before it’s effectively coded! Reusability? Once validated, I’ll use this artefact to build a robust test-suite that will be automated to validate my development. I’m also building a really good artefact to detect possible issues and impacts with some change requests. Much more than a test that I’ll through away within 10 days. Still not convinced? Have you noticed that I’m not writing documentation … My documentation are my test-cases. With just playing the test-suites, I can confirm that my documentation is inline with my development … living and always up-to-date documentation is priceless.




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