Integration Testing: Definition, Types & Examples


Integration Testing: Definition, Types & Examples


What is Integration Testing?

Integration testing is a type of testing in which software modules are logically integrated and tested as a group. A typical software project consists of several software modules written by various programmers. The goal of this level of testing is to identify flaws in the interaction of these software modules when they are combined.

Integration testing examines data communication between these modules. As a result, it is also known as “I&T” (Integration and Testing), ‘String Testing’ and sometime ‘Thread Testing.’

Why should you perform Integration Testing?

Software Testing Levels

Although each software module is unit tested, defects do exist for a variety of reasons, including:

  • In general, a Module is created by an individual software developer whose understanding and programming logic may differ from that of other programmers. Integration testing is required to ensure that the software modules work together.
  • There is a high possibility of client requirements changing during module development. Because these new requirements may not be unit tested, system integration testing is required.
  • Interfaces between software modules and databases may be incorrect.
  • External hardware interfaces, if present, could be incorrect.
  • Inadequate exception handling may cause problems.

Integration Test Case Example

The Integration Test Case differs from other test cases because it focuses on the modules’ interfaces and data/information flow. Priority should be given to integrating links rather than unit functions that have already been tested.

Integration Test Case Examples for the Following Scenario: The application has three modules: ‘Login Page,’ ‘Mailbox,’ and ‘Delete Emails,’ all of which are logically integrated.

Because it has already been done in Unit Testing, do not focus much on Login Page testing here. However, note how it is linked to the Mail Box Page.

Mail Box: Examine its integration with the Delete Mails Module.

Test Case ID Test Case Objective Test Case Description Expected Result
1 Check the interface link between the Login and Mailbox module Enter login credentials and click on the Login button To be directed to the Mail Box
2 Check the interface link between the Mailbox and Delete Mails Module From Mailbox select the email and click a delete button Selected email should appear in the Deleted/Trash folder

Read more: Unit Testing in Software Testing: Types, Tools & Best Practices

Integration Testing Types

Software engineering defines several strategies for carrying out integration testing, such as:

  •  Big Bang Approach:
  •  Incremental Approach: which is further divided into the following
    • Top Down Approach
    •  Bottom-Up Approach
    •  Sandwich Approach – Combination of Top Down and Bottom Up

The following are the various strategies, their implementation, and their limitations and advantages.

Big Bang Testing

Big Bang Testing is an approach to integration testing in which all components or modules are integrated simultaneously and then tested as a unit. During testing, this combined set of components is treated as an entity. The integration process will fail if all of the components in the unit are not completed.

Advantages: Ideal for small systems.


  • Localization of faults is difficult.
  • Given the sheer number of interfaces that must be tested in this Approach, some interfaces may be overlooked.
  • Because integration testing can only begin after “all” modules have been designed, the testing team will have less time for execution during the testing phase.
  • Because all modules are tested at the same time, high-risk critical modules are not isolated and tested first. Peripheral modules dealing with user interfaces are also not isolated and prioritized for testing.

Incremental Testing

The Incremental Testing approach involves integrating two or more modules logically related to each other and testing the application for proper operation. The other related modules are then incrementally integrated, and the process is repeated until all logically related modules have been successfully integrated and tested.

The Incremental Approach, on the other hand, is carried out by two different methods:

  • Bottom Up
  • Top Down

Bottom-up Integration Testing

Bottom-up Integration Testing

Bottom-up Lower level modules are tested first in an integration testing strategy. These tested modules are then used to speed up the testing of higher-level modules. The process is repeated until all top-level modules have been tested. The next level of modules is formed after the lower level modules have been tested and integrated.

Diagrammatic Representation:


  • Fault localization is easier.
  • Unlike the Big-bang approach, no time is wasted waiting for all modules to be developed.


  • Critical modules (at the highest level of software architecture) that control the application flow are tested last and may have flaws.
  • An early prototype is not possible.

Top-down Integration Testing

Top-down Integration Testing

Top Down Integration Testing is a method of performing integration testing from top to bottom following the control flow of a software system. Higher-level modules are tested first, followed by lower-level modules to test the software functionality. If some modules are not yet ready, stubs are used for testing.

Diagrammatic Representation:


  • Fault Localization is easier.
  • Possibility to obtain an early prototype.
  • Critical Modules are tested on priority; major design flaws could be found and fixed first.


  • Needs many Stubs.
  • Modules at a lower level are tested inadequately.

Sandwich Testing

Sandwich testing is a strategy in which top-level modules are tested alongside lower-level modules. In contrast, lower modules are integrated and tested as a system. Because it combines top-down and bottom-up approaches, it is known as Hybrid Integration Testing. It employs the use of both stubs and drivers.

Sandwich Testing
Sandwich Testing

Stubs and Drivers

Stubs and Drivers are dummy programs used in integration testing to help with software testing. These programs serve as stand-ins for missing models in testing. They do not implement the entire software module’s programming logic but instead simulate data communication with the calling module while testing.

  • Stub: Is called by the Module under Test.
  • Driver: Calls the Module to be tested.

Read more: What is Regression Testing? Definition, Tools and How to Begin

How to Perform Integration Testing

Regardless of the Software testing strategies (discussed above), the Integration test procedure is as follows:

  1. Make a plan for the integration tests.
  2. Creating Test Scenarios, Cases, and Scripts
  3. Running the test Cases is followed by defect reporting.
  4. Defect tracking and re-testing
  5. Steps 3 and 4 are repeated until integration is completed.

A Synopsis of Integration Test Plans

It has the following characteristics:

  • Testing Methods and Approaches (as discussed above).
  • Integration Testing Scopes and Out-of-Scope Items
  • Roles and Responsibilities
  • Integration testing prerequisites
  • Environment for testing
  • Risk and Mitigation Strategies

Integration Testing Entry and Exit Criteria

Entry Criteria:

  • Components/Modules That Have Been Unit-Tested
  • All High Priority bugs have been fixed and closed.
  • All modules must be coded and successfully integrated.
  • Plan, test cases, and scenarios for integration tests must be signed off and documented.
  • Integration testing necessitates the establishment of a test environment.

Exit Criteria:

  • Successful Testing of Integrated Application.
  • Executed Test Cases are documented.
  • All High prioritized bugs were fixed and closed.
  • Technical documents to be submitted, followed by release Notes.

Best Practices/ Guidelines for Integration Testing

  • Determine the Integration Test Strategy that could be used first, and then prepare the test cases and data accordingly.
  • Examine the application’s architecture design and identify the critical modules. Priority should be given to testing these.
  • Obtain the interface designs from the Architectural team and write test cases to test all of the interfaces thoroughly. The database/external hardware/software application interface must be thoroughly tested.
  • The test data comes second to the test cases in importance.
  • Before executing, always have the mock data ready. When running the test cases, do not select test data.

I am currently the SEO Specialist at Bestarion, a highly awarded ITO company that provides software development and business processing outsourcing services to clients in the healthcare and financial sectors in the US. I help enhance brand awareness through online visibility, driving organic traffic, tracking the website's performance, and ensuring intuitive and engaging user interfaces.