Unit Testing vs Functional Testing: A Comparative Guide

Ryan Williamson
3 min readJan 4, 2022

A key part of building a high-quality software solution is all the software testing that goes into it. The role of the developer becomes critical in the development cycle to perform testing well during the level of system testing.

You would agree the main goal of any testing is to deliver a quality product that finds the right balance between unit testing and functional testing.

Functional testing vs unit testing can be considered as the foundation of the testing process. However, companies often struggle to decide which form of testing is better suited for their project; in this article, we will discuss the two most basic forms of software testing, i.e. unit testing and functional testing, and then help you understand how to make an informed choice between the two.

Unit testing: This software testing method wherein individual units of code are tested in isolation to determine the API’s smallest testable parts and ensure they function as intended even in isolation.

  • Unit testing enables developers to not only refine the code but also ensure the module works as intended and as productively as possible.
  • This type of testing also allows teams to test only specific parts of the software without needing to wait for the rest of the parts and project to be completed.

Functional testing: When a software testing team runs tests to analyze the software’s functional performance based on the intended users’ requirements and expectations, the process is called functional testing.

  • This type of testing is highly conducive to ensuring the development team is successfully able to fulfill not only the client’s requirements and expectations but also those of the clients they eventually intend to serve.
  • Functional testing empowers the team charged with software development to incorporate user perspective while developing test scenarios that exemplify real-world used scenarios.
  • Such testing is also used by developers to scale up the system’s actual usage via improvement of the software product’s quality.

Now allow us to quickly compare these two test types to help you make an informed decision.

  1. Coverage: With unit testing, developers can achieve high code coverage which, in turn, supports the conclusion that the project has been properly developed and maintained. Whereas with functional testing, test coverage seeks to sync the project’s requirements and the test cases.
  2. Purpose: Developers use unit testing to establish a sturdy codebase without necessitating humongous investments. Such tests also supply documentation for high-level testing, such as functional testing, integration testing, etc., further on in the development process. The key goal of functional testing is to analyze all the functionalities of the given system. This type of testing involves close evaluation of the application, the networking infrastructure, the hardware, etc.
  3. When?: Some are inclined to believe that unit tests can be used in place of functional testing: this is not true. Both types of testing serve different purposes: unit tests should ideally start being written right along with the start of the development project since it allows developers to not only refactor the code but also determine if any part of the code has been inadvertently broken. Unit testing is followed by functional testing which should be started when two modules in the code end up engaging and interacting with each other.

We understand choosing between these two types of tests may seem like a difficult choice at first. However, careful analysis and comparison of the two test types, including your project’s unique requirements, will help you decide if you should opt for unit testing or if software functional testing will be better suited for your project.

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Ryan Williamson

A professional and security-oriented programmer having more than 6 years of experience in designing, implementing, testing and supporting mobile apps developed.