Functional and Non-Functional Requirement In Software Testing

Introduction to Functional and Non-Functional Requirement In Software Testing:

Requirements form the basis for initiating any task. When there is a need, then we devise an action plan and proceed towards its accomplishment. The process of software development commences with only one factor in mind - purpose of developing an application.

Hence requirements for a software can be classified in two broad categories- functional, non-functional.

Functionality simply states the expected results from the system and non functional requirements are the obvious features that are expected from the application.

Let us understand these two terms in further detail.

1. Functional Requirements:

These type of requirements can be thought of as an 'objective' of the software product to be built. The functional requirements form the core of the entire software development process. When a software project is undertaken, the functionalities it must serve, are clearly outlined in the requirements specification document.

It is very important to understand what the client's needs are, the need for a software product, output expected from the system. In short, the key functionalities a software system must deliver.

Functionality can be understood in the context of a real world scenario. For instance, one needs an application to calculate the price for selected products and generate an invoice for the same. The application should also be able to integrate components such as comparison of one product with another similar one of a different brand, and list comparisons to enable the user to make a wise choice. Such facilities can be termed as functional requirements.

Functional requirement is supposed to adhere to some basic ground rules:

  • Functional requirements to be met should be aligned with the business requirements.
  • Timely review of the functionalities to ensure that the project is moving in the right direction.
  • Adhering to rules and policies, and not leaking information to any external sources.

2. Non-Functional Requirements:

These set of requirements are an extension to the functional requirements. Non functional requirements are not the ones that a user demands, but is implicitly expected from the application developed so far. It can be thought of as the “efficiency” of the application in terms of its performance. This term can be further elaborated in the light of a simple fact.

When we order food online, the food has to be the one that is selected, but beyond that many companies offer delivery within 30 minutes , else, free delivery. This free delivery can be thought of as a non functional requirement which extends beyond providing the basic functionality, that is food delivery.

Similarly following factors form the major areas which constitutes a set of non functional requirements.

  • Efficiency - It is the parameter to measure the performance of the software application.
  • Quality - Quality is the overall factor contributing to non functional requirement. A quality end product is what everyone demands.
  • Response Time - The time taken to perform an action triggered by the user.
  • Availability - The extent to which a system is available for use initially. If more technically defined then it can be stated as the proportion of time a system is in functioning condition.
  • Interoperability - Easy to use interface that should enable the user to work with any product with ease.
  • Security- Application should not be vulnerable to any exploitation. That is, strict authentication mechanisms to be applied to the system.
  • Fault Tolerance- A major aspect of any software product. It portrays the capability of a system to continue performing in the event of failure of some other components.
  • Documentation - Provides an overview about the system, clearly lays down the specifications in detail.

Functional and non-functional requirements adheres to the following types of testing:

  1. Functional Test Included are:
  2. Non-Functional Test Included are:

Functional and Non-Functional Testing

The characteristics of 'functional' and 'non-functional' requirements are governed by the types of testing' mentioned above as they are crucial in determining the validity of the respective requirement specifications.

A functional requirement must cater to more granular level needs whereas non-functional requirements are at the macro level.


Functional requirements are characterised by the core or the basic operations, an application is expected to deliver, such as order, purchase, place order etc. On the contrary non-functional requirements comprise of the extra or precisely the external factors that lay a foundation for an application, say, how scalable an application is to be able to adapt to varying user loads, reliability to ensure that the application isn't vulnerable to frequent malware attacks, delivers a consistent performance and so on.

Thus requirements for functional and non-functional aspects are inseparable to ensure an application's sustenance in the long run.

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