Structural Testing vs Functional Testing

Difference between Structural and Functional Testing

In this article, we will study the difference between structural and functional testing. Before we start with the difference, let us first understand both types of testing in detail.

Definition of Structural Testing

Structural testing is a type of software testing that tests the internal code structure of the software. It verifies what happens inside the system and is also referred to as white-box or clear-box testing.

This type of testing requires good knowledge of the programming language and the code’s internal implementation. It is based on how the system functions rather than the business requirements.

Different Types of Structural Testing Techniques

  1. Mutation – A small change in the source code is made to test if the test cases can detect the changes. It is also called fault-based testing, as the fault is intentionally created in the code. 

  1. Control flow – This type of structural testing uses the program’s control flow as a model. Complete knowledge of the structure, design, and code of the software is necessary for this type of testing.

  1. Slice-based – Slice-based testing divides the code into small modules called slices and tests the slice that can have a major impact on the entire software.

  1. Data flow – Data flow testing depends on data values and uses control flow graphs to identify any bugs that can interrupt data flow.

Definition of Functional Testing

Functional testing is software testing that checks the functionality of the software application as per the requirement specification. It validates the output against the given input.

Functional testing aims to check the necessary usable function, input validation, and functional completeness. It is concerned with user experience and application function rather than the coding aspects. 

Different Types of Functional Testing

  1. Unit testing – As the name suggests, the smallest units of the system are tested. Unit testing checks different application parts and ensures each unit is working fine. The main purpose is to ensure that a unit functions as intended and generates the expected output against the given input.

  1. Integration testing – Individual units are integrated and tested to evaluate the interaction between them. Integration testing validates that the units as a group functions correctly.

  1. System testing – The entire system as an integration unit is tested to verify all business and functional requirements are met. An end-to-end system setup is required and is performed before User Acceptance Testing. The test environment for system testing must be a replica of the production environment.

  1. Acceptance testing – Acceptance testing by the end-user to clarify that the developed system fulfills all the requirements as per the SRS document. The final testing phase is performed just before release to the real world. The application’s acceptance or rejection depends on the performance of acceptance testing. 

  1. Regression testing – Regression testing ensures that the new changes have not affected the existing functionalities or introduced a new defect. 

  1. Sanity testing – Sanity testing is performed on a new build with new code or small bug fixes. It focuses on the areas affected by the new code or bug fixes. 

  1. Smoke testing – This testing technique ensures that all the major end-to-end functionality of the application works as intended. It is also called Build Verification Testing, as smoke testing adds a verification layer to check whether the new build can proceed or has to be redone. 

  1. Recovery testing– Recovery testing aims to verify the system’s ability to recover from testing failures like crashes and other issues. 

Structural Testing vs Functional Testing

Structural TestingFunctional Testing
This test evaluates the code structure or internal implementation of the code.This test checks whether the software is functioning in accordance with functional requirements and specifications.
It is also known as white-box or clear-box testing as thorough knowledge and access of the code is required. It is also known as black-box testing as no knowledge of the internal code is required.
Finds errors in the internal code logic and data structure usage.It ensures that the system is error-free.
It does not ensure that the user requirements are met.It is a quality assurance testing process ensuring the business requirements are met.
Performed the entire software in accordance with the system requirements.Functional testing checks that the output is given as per expected.
Testing teams usually require developers to perform structural testing.A QA professional can simply perform this testing.
Perform on low-level modules/software components.The functional testing tool works on event analysis methodology.
It provides information on improving the internal structure of the application.It provides information that prevents business loss.
Structural testing tools follow data analysis methodology.Functional testing tool works on event analysis methodology.
Writing a structural test case requires understanding the coding aspects of the application.Before writing a functional test case, a tester is required to understand the application’s requirements.
It examines how well modules communicate with one another.It examines how well a system satisfies the business needs or the SRS.


Software testing is important to identify bugs, improve product quality and detect security vulnerabilities. Functional testing determines how well the application performs based on customer requirements, whereas structural testing verifies the implementation of the code structure.

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