Unit Testing vs Functional Testing

Posted on by By K Ramakrishna, in Software Testing | 0

Unit Testing v/s Functional Testing

Unit tests meant for a developer that the code is doing things right; functional tests meant for a developer that the code is doing the right things.

Unit Tests are written from a programmers perspective. They are made to ensure that a particular method (or a unit) of a class performs a set of specific tasks.

Functional Tests are written from the user’s perspective. They ensure that the system is functioning as users are expecting it to

Unit tests:

A unit is the smallest testable part of an application like functions, classes, procedures, interfaces. Unit testing is a method by which individual units of source code are tested to determine if they are fit for use. Unit tests are basically written and executed by software developers to make sure that code meets its design and requirements and behaves as expected.

The goal of unit testing is to segregate each part of the program and test that the individual parts are working correctly.This means that for any function or procedure when a set of inputs are given then it should return the proper values. It should handle the failures gracefully during the course of execution when any invalid input is given

Advantages of Unit testing:

1. Issues are found at early stage. Since unit testing are carried out by developers where they test their individual code before the integration. Hence the issues can be found very early and can be resolved then and there without impacting the other piece of codes.

2. Unit testing helps in maintaining and changing the code. This is possible by making the codes less interdependent so that unit testing can be executed. Hence chances of impact of changes to any other code gets reduced.

3. The cost of fixing a defect detected during unit testing is lesser in comparison to that of defects detected at higher levels. Compare the cost (time, effort, destruction, humiliation) of a defect detected during acceptance testing or when the software is live.Since the bugs are found early in unit testing hence it also helps in reducing the cost of bug fixes. Just imagine the cost of bug found during the later stages of development like during system testing or during acceptance testing.

4. Unit testing helps in simplifying the debugging process. If suppose a test fails then only latest changes made in code needs to be debugged.Debugging is easy. When a test fails, only the latest changes need to be debugged.

Functional tests:

Functional tests are conducted to ensure the system behaves according to the functional requirements.  Use cases are developed to validate that all functions outlined in the requirements are present in the system and work as intended.  This testing should not be performed by the people who built the system.

Functions (or features) are tested by feeding them input and examining the output. Functional testing ensures that the requirements are properly satisfied by the application. This type of testing is not concerned with how processing occurs, but rather, with the results of processing.

During functional testing, Black Box Testing technique is used in which the internal logic of the system being tested is not known to the tester.Functional testing is primarily is used to verify that a piece of software is providing the same output as required by the end-user or business. Typically, functional testing involves evaluating and comparing each software function with the business requirements. Software is tested by providing it with some related input so that the output can be evaluated to see how it conforms, relates or varies compared to its base requirements.


No matter how clever we are at building the projects we work on, no matter how flexible the systems are that we build, if what we produce isn’t usable, we’ve wasted our time. As a result, functional testing is the most important part of development.Because both types of tests are necessary, you’ll need guidelines for writing them.


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