Today’s consumers want more software, they want it to do more, and they want it now. As a result, some developers are tempted with the idea of rushing through testing, figuring it’s better to release a piece of inferior software on the release date (or close to it as possible) than to suffer through a long delay.

However, bug-ridden software can lead to a catastrophic public relations nightmare and backlash. So, developers need to release software and apps that have undergone thorough, rigorous testing.

To that end, today, we are focusing on one specific aspect of testing: integration testing. This article defines integration testing, why it’s needed, the correct approaches, the best integration testing techniques, a look at the tools and practices, and even an example of integration testing.

Without further ado, let’s start things with a definition. What is integration testing anyway?

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What Is Integration Testing?

Integration testing is known as the second level of the software testing process, following unit testing. Integration testing involves checking individual components or units of a software project to expose defects and problems to verify that they work together as designed.

As a rule, the usual software project consists of numerous software modules, many of them built by different programmers. Integration testing shows the team how well these disparate elements work together. After all, each unit may function perfectly on its own, but the pressing question is, “But can they be brought together and work smoothly?”

So, integration testing is the way we find out if the various parts of a software application can play well with others!

Why Perform Integration Testing?

Other than the fundamental truth that developers must test all software applications before releasing them to the public, there are some specific reasons why developers should perform integration testing.

  • Incompatibility between software modules can cause errors
  • Developers must confirm that every software module can interact with the database
  • Requirements change, thanks to client input. However, maybe those new requirements haven't been thoroughly tested yet and should be
  • Every software developer has their understanding and programming logic. Integration testing ensures that these various units function smoothly
  • There may be potential problems with hardware compatibility
  • Modules often interact with third-party APIs or tools, so we need integration testing to verify that the data these tools accept is correct

Advantages of Integration Testing

  • Integration testing ensures that every integrated module functions correctly
  • Integration testing uncovers interface errors
  • Testers can initiate integration testing once a module is completed and doesn’t require waiting for another module to be done and ready for testing
  • Testers can detect bugs, defects, and security issues
  • Integration testing provides testers with a comprehensive analysis of the whole system, dramatically reducing the likelihood of severe connectivity issues

Challenges of Integration Testing

Unfortunately, integration testing has some difficulties to overcome as well.

  • If testing involves dealing with two different systems created by two different vendors, there will be questions about how these components will affect and interact with each other
  • Integrating new and legacy systems demands many testing efforts and potential changes
  • Integration testing becomes complex due to the variety of components involved (e.g., platforms, environments, databases)
  • Integration testing requires testing not only the integration links but the environment itself, adding another layer of complexity to the process

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What’s the Difference Between Integration Testing and System Testing?

Integration testing runs unit tests on one or a few integrated modules to verify if the integrated modules work as designed or not. On the other hand, system testing tests the entire system, seeing if the system works in harmony with all the integrated modules and components.

Guidelines for Integration Testing

If you are attempting integration testing, keep these guidelines in mind:

  • First, don’t initiate integration testing until each module has undergone functional testing first
  • Module testing should follow an accepted sequence not to overlook any integration scenarios
  • Agree on a test case strategy to prepare and execute test cases in conjunction with the test data
  • Study the application’s architecture and structure, identifying the most important modules to be tested first. Also, identify every possible scenario
  • Design test cases that will create detailed interface verification
  • Input data is vital to conducting reliable integration testing, so choose test case execution input data wisely
  • Generate reports on any bugs found. Send bug reports to the developers, have them fix the errors, then conduct testing again

Regarding Various Integration Testing Techniques

Developers can use many different accepted software testing techniques in integration testing. Here’s a collection of some of the common techniques available from the field of software testing. These techniques are not to be confused with integration testing types, which we’ll cover the following section.

Black Box Testing

  • All-pairs Testing
  • Boundary Value Analysis
  • Cause and Effect Graph
  • Decision Table Technique
  • Equivalence Partitioning
  • Error Guessing
  • State Transition technique

White Box Testing

  • Branch Coverage Testing
  • Control Flow Testing
  • Data flow testing
  • Decision Coverage Testing

Types of Integration Testing

Here are the six most popular forms of integration testing.

Big Bang Method

This method involves integrating all the modules and components and testing them at once as a single unit. This method is also known as non-incremental integration testing.

Bottom-Up Method

This method requires testing the lower-level modules first, which are then used to facilitate the higher module testing. The process continues until every top-level module is tested. Once all the lower-level modules are successfully tested and integrated, the next level of modules is formed.

Hybrid Testing Method

This method is also called "sandwich testing." It involves simultaneously testing top-level modules with lower-level modules and integrating lower-level modules with top-level modules, and testing them as a system. So, this process is, in essence, a fusion of the bottom-up and top-down testing types.

Incremental Approach

This approach integrates two or more logically related modules, then tests them. After this, other related modules are gradually introduced and integrated until all the logically related modules are successfully tested. The tester can use either the top-down or bottom-up methods.

Stubs and Drivers

These elements are dummy programs used in integration testing to facilitate software testing activity, acting as substitutes for any missing models in the testing process. These programs don’t implement the missing software module’s entire programming logic, but they do simulate the everyday data communication with the calling module.

Top-Down Approach

Unlike the bottom-up method, the top-down approach tests the higher-level modules first, working the way down to the lower-level modules. Testers can use stubs if any lower-level modules aren’t ready.

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A Guide to Integration Testing Tools

Software testers have access to a wide variety of testing tools. Here’s a sample.

Citrus

Citrus is an open-source testing framework ideal for complex integration testing. It supports multiple protocols like HTTP, JMS, and SOAP.

Unique Features

  • Features error recreation
  • Cost-effective
  • Allows testers to validate the database
  • Offers test plans and test coverage documentation

Ldra

This tool offers several integration testing tool sets that match the compliance standards of different organizations. In addition, Ldra is an open-platform tool that provides code coverage analysis, design reviews, dynamic analysis and static/dynamic analysis, and much more.

Unique Features

  • Automates approval evidence and software certification
  • Provides seamless execution of integration and unit testing
  • Provides common environment support suitable for integration testing for many different projects

Protractor

This open-source automation testing tool is designed for web-based application testing. Although specifically designed for Angular and AngularJS applications, its use case isn’t limited to those applications. Protractor enjoys support in many different browsers, including Chrome, Firefox, Internet Explorer, and Safari.

Unique Features

  • Performs testing from the perspective of the end-user
  • Ideal for end-to-end integration and dynamic web application testing
  • Allows you to execute multiple instances of an application

Tessy

Tessy is designed especially for embedded software and handles every aspect of the test organization, including management, traceability, and requirements.

Unique Features

  • Supports popular programming languages such as C and C++
  • Multiple users can access the tool through just one license
  • Provides a comprehensive test report

VectorCast/Ada

This testing tool works for both unit and integrating testing projects, significantly reducing costs and time by automating much of the testing process. It also uses stubs and drivers to create missing modules to simulate code functionality.

Unique Features

  • Provides test case reusability suitable for regression testing
  • Automatic stubs and drivers code generation
  • Integrates well with multiple tools like Green Hills and IBM Rational

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Best Practices for Integration Testing

Before you begin integration testing, keep the following best practices in mind.

Initiate integration testing as soon as possible

Thanks to today’s Agile methodology, developers can conduct integration testing earlier in the project. This fact means they can find bugs and integration issues sooner, ensuring a faster release to the public.

Determine which testing strategy you want to use

Some testing strategies work better with specific development projects. Use your experience to decide which one to go with.

Study the application’s architectural design and identify the critical modules

Critical elements must take priority.

Make sure you have mock data at hand

Mock data should be prepared before testing. Don’t choose test data when you’re running test cases.

Take and keep notes. Log extensively

The only way you can discover problems that show up in testing is by logging your test results. Everything should be documented, so developers can consult the results and see what went wrong.

A Quick Description of Integration Test Plans

A good integration test plan has the following attributes:

  • Methods and approaches to testing
  • Prerequisites for integration testing
  • Roles and Responsibilities
  • Integration testing scopes and out-of-scopes items
  • A good testing environment
  • Risk and mitigation plans

Entry and Exit Criteria of Integration Testing

Here are the criteria that should be met before starting integration testing and before ending it.

Entry Criteria

  • The integration test plan document is approved, signed off, and documented.
  • All necessary integration test cases have been prepared.
  • The test data has been created.
  • Developed modules and components unit testing has been completed.
  • All the critical and high-priority defects are fixed and closed.
  • The required test environment has been set up for integration testing.

Exit Criteria

  • All the integration test cases have been successfully executed.
  • There are no open critical or priority P1 and P2 defects.
  • The test documents have been prepared.

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An Example of Integration Testing

Here’s an example of integrating testing involving a website that features “Log-in Page,” “Mailbox,” and “Delete E-mails” functions.

Test Case ID

Test Case Objective

Test Case Description

Expected Result

1

Validate the log-in and the mailbox’s module interface link

Enter the required log-in credentials and click the log-in button

Control is transferred to the mailbox

2

Validate the mailbox and the Delete Mails Module interface links

Select an e-mail from the mailbox, then click on "delete."

Chosen e-mail is sent to the Deleted/Trash folder.

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About the Author

John TerraJohn Terra

John Terra lives in Nashua, New Hampshire and has been writing freelance since 1986. Besides his volume of work in the gaming industry, he has written articles for Inc.Magazine and Computer Shopper, as well as software reviews for ZDNet. More recently, he has done extensive work as a professional blogger. His hobbies include running, gaming, and consuming craft beers. His refrigerator is Wi-Fi compliant.

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