Difference Between Structural and Functional Testing

Difference Between Functional And Structural Testing: Structural and functional testing is a form of testing performed to evaluate the response of software & computer hardware to various stimuli.

In Structural Testing, software application functionality is verified by performing tests that exercise each individual module in isolation. Each module can be tested independently. Functional Testing verifies it by performing tests that exercise specified combinations of related modules. It is performed to verify whether the software meets the expected requirements and to detect functional errors.

Structural Testing

Structural testing is a black-box testing method or software testing technique in which software’s structural elements, such as modules, components, and objects, are tested for proper interface and interaction.

Structural Test is performed without seeing the internal implementation details of the code structure. The main goal is to see how the system works, not just if it meets business requirements. There are four types of structural testing techniques:

Mutation testing
Control flow testing
Data flow testing
Slice-based testing

Mutation Testing

Small modifications or “mutations” are intentionally introduced into the source code to see if the test cases detect them. Finding the mutations demonstrates the quality and comprehensiveness of the tests.

Control Flow Testing

The program’s control flow structure is used as a model to derive test cases. It requires extensive knowledge of the code and design. The goal is to execute all paths through the code at least once.

Data Flow Testing

The code is analyzed to trace the life cycle of data values. Control flow graphs identify points where bugs could potentially interrupt or contaminate data as it flows through the system.

Slice-Based Testing

The code is segmented into “slices” – small modules that can impact the overall software behaviour. Each slice is tested independently and thoroughly.

The key focus across all structural testing techniques is leveraging internal software knowledge to verify code modules’ correct functioning and interactions methodically. Thorough structural testing improves quality by revealing faults early.

Functional Testing

Functional testing is a type of black-box testing that bases its test cases on the specifications of the software component being tested. It determines if the component under test behaves as specified in the functional specification or user requirements document. It executes representative input sequences corresponding to the desired functional requirements.

Functional testing has five levels – Unit, Integration, System, Acceptance, and Regression:

Unit Testing

Unit testing verifies whether each software module works as expected by performing a set of test cases on the individual modules. It focuses mainly on individual components, methods, classes, or functions. Unit testing is performed after module coding and before integration testing.

Integration Testing

All the modules are tested in integration testing to verify whether they operate correctly when combined with other software modules.

System Testing

In system testing, it is verified whether the entire integrated application meets the requirements of its users and works as expected.

Regression Testing

In regression testing, whether changes to the software components have not affected the existing functionalities and features are verified. It is performed after every major code change.

Acceptance Testing

In acceptance testing, it is verified whether specified users are satisfied with the application’s functionality & performance.

Difference Between Structural and Functional Testing

Here are some of the differences between the two:

AspectStructural TestingFunctional Testing
Manual/Automatic ModeStructural testing is done in manual mode.Functional testing can be performed either manually or automatically.
Design BasisStructural test cases are designed based on external specifications, and internal code structure is not considered.Functional testing would depend on both external specifications and the internal workings of the component.
Test Case BasisStructural test cases are based on input/output conditions.Functional test cases are based on actions that a component can perform.
PurposeStructural testing finds errors in data structure usage and internal coding logic.Functional testing verifies that the system adheres to acceptable standards of information processing and does not contain any defects.
Timing of TestingStructural testing is done after the coding process is completed by maintenance groups.Functional testing is performed during development and/or maintenance.
Dependency on Data ValuesStructural test cases do not depend on data values.Functional test cases may have to use some specific value for a test case to pass or fail (error checking).
Error Checking LevelStructural test cases are based on hardware-level error checking.Functional testing is achieved by software techniques.
Data Structures FocusStructural testing involves static data structures and algorithms.Functional testing involves the analysis of dynamic data structures and object-oriented programming.
Purpose of TestingStructural testing addresses error detection and repair.Functional Testing may address quality attributes such as reliability, maintainability, security, etc.
Focus on BugsStructural testing mainly focuses on logical errors or bugs in the code.Functional testing focuses on verifying that the system meets its requirements.
Testing Tool BasisThe structural Testing tool is based on data flow analysis methodologies.The functional Testing tool is based on the Event Analysis methodology.
Application Elements TestedStructural Testing is used to test the functional elements of an application, such as a text display feature and how it works with other features.Functional Testing is carried out based on the business requirements of the application and looks at the user’s acceptance criteria to how well the system meets the user’s needs.
Module/Software Component LevelStructural Testing is performed on low-level modules/software components.Functional Testing is performed on the entire software system as per required specifications.
Boundary ConditionsStructural testing does not recognize any boundary conditions as per requirement criteria.Functional testing accepts all boundary conditions.
Focus on Actions or I/O ConditionsStructural Testing looks at input/output conditions rather than actions that a component can perform.Functional Testing is concerned with the way an application behaves in terms of its business domain and satisfies the user’s needs.
Intercommunication vs. Business PurposeStructural Testing is mainly used for testing intercommunication between modules.Functional Testing would look at how well the system satisfies a certain business purpose or set of business purposes.
Objective Criteria for Pass/FailFunctional Testing has objective criteria to pass or fail.Structural Testing may have some subjective interpretation of the result.
Test Case DesignersStructural Test Cases are usually carried out by a software development group.Functional test cases are designed by business analysts and testers.
Information ProvidedStructural Testing provides information about the internal design of the module being tested, contributing to improving the internal design.Functional Testing provides information about how well the system meets the user’s needs and helps in discovering defects that may lead to business loss.
Scope of ApplicationStructural Testing is used for testing systems that are interconnected.Functional testing could be used to test stand-alone applications.


Structural Testing and Functional Testing are used for different purposes. Both types of testing are important in their own way to get robust software applications, but these two types of testing are quite different.

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