Functional and Non Functional Testing - Difference with Real life example

It is common in testing project to scope of testing in the project is to perform functional as well as non-functional testing in the project. It is important to understand the difference between the two to define strategies for each testing. Let me try to explain this with a simple example in daily life. Suppose I have to test the functional and non-functional requirement of a restaurant.

The functional requirement can be following

When a user enters the restaurant, he will be welcomed by the Staff.  User will place the order; Order will be delivered to User. Once user completes the dinner/lunch, he will pay either by cash or credit card. Staff will say goodbye to user once user exits from the restaurant.

The above is an example of functional requirement in real price, similar in software can be compared to an online e-commerce site.

The functional requirement will be broken down into functional test scenarios which can further be broken down into test cases ensuring all the requirement are covered using RTM (Requirement traceability matrix).

Now coming to the same example, Let us talk about the non-functional requirement in the same example.User will be very much influenced by time it takes from the time he places the order to time order reaches him. This is related to performance and efficiency aspect of requirement.

Similarly there can be security compromise, suppose I pay my bill by credit card and the staff instead of returning the bill with credit card to me, give it to some other customer, and the customer exits with my credit card and spends money from my card. This is an example of Security testing.

Let us take another example, suppose I ordered a dish which needs long cooking, Suppose the food is undercooked. Although I received what I ordered, the food is such that, if I eat it, It will take me one week to recover from its after effect. This is an example of usability testing.

As we see in the example, Non-Functional features (features that were not a part of functional requirement) are very important and needs to be properly tested to ensure the business success.

As in above example, If any one of the performance, security and usability of the restaurant does not meet the customer requirement, There is high probability, the customer will never visit the restaurant again, which will be a business loss to the restaurant.

The same example can be easily reciprocated in software projects. Therefore non-functional testing should be given proper priorities before releasing a project. How much to spend on non functional testing depends on which non-performance parameters are critical.

For e.g in a trading site, security testing should be preference, while in a search engine, e.g. google, the performance, load, stress testing are more important.

Some examples of Non functional includes:

• Usability Testing

• Security Testing

• Performance testing

• Load Testing

• Stress testing

• Scalability Testing

• Data Integrity Testing

• Interoperability Testing