What is Integration Testing?

Introduction

In this article, we will discuss Integration testing in detail, starting from its definition, its importance, and how it works. We will also examine the components involved in Integration testing, key steps to follow, the main types of integration testing, and the applications of Integration testing in software development.

Before we proceed, what exactly is software testing?

Software testing refers to evaluating a software application to identify issues before releasing it to the users. This ensures the release of quality software that meets user expectations and performance requirements.

Integration testing is a part of a software testing strategy known as the Testing Pyramid. This strategy is illustrated below.

It has end-to-end (E2E) tests at the top, integration tests in the middle, and unit tests at the bottom, and is explained as having many unit tests, fewer integration tests, and even fewer E2E tests in your system.

What is Integration Testing?

Integration testing is a type of software testing that involves testing how various software parts work together as a whole. Its main focus is on how different components of the software interact.

The image below is a simple illustration of an integration test in software development.

The service block (in blue) represents any backend functionality or logic, for example, userService, orderService, and so on. This would be the code for creating users, processing data, or managing requests.

The database (in orange) is where the data is stored, for example, user records, orders, and so on.

The arrow indicates interaction between the two components; that is, the service communicates with the database, for example, storing or retrieving data.

Thus, an integration test would check whether the service is correctly sending data to the database, whether the database is responding correctly, and whether both work as expected.

Integration tests like the one illustrated above help catch issues that unit tests might have missed, like misconfigured database queries and connection problems

Why is Integration Testing Important?

Integration testing is a crucial step in the software development life cycle, so you must be asking yourself why and how. Below, let’s discuss some of the reasons why Integration testing is important.

• Early detection of issues. Integration testing helps identify bugs in interactions between components/modules. This helps save costs that could be incurred from later fixes.

• Improves system reliability. Integration testing verifies that integrated components work seamlessly without any errors. This increases trust and makes the system reliable as it behaves as expected in real-world conditions.

• Improves software quality. The fact that the integrated components/modules are tested to ensure that they work as expected means the software application is bug-free and thus of better quality.

• Prepares for system testing. It is a process that prepares the software under development for system and acceptance testing, thus reducing bugs found in later testing stages.

How to Write Integration Tests?

Integration testing ensures that different components of a software work perfectly together. To write integration tests, you need to follow the following procedure.

1. Start by determining which of the software components need to be integrated.

2. Select a type of integration test you want to implement, choosing from the big-bang approach, bottom-up, top-down, or mixed integration testing.

3. Create your test cases by defining the inputs and expected outputs of various components and their interactions with each other.

4. Set up your test environment by simulating real-world conditions, for example, use mock servers for external APIs like payment gateways, configure a test database like PostgreSQL in a Docker environment, etc.

5. Run the tests and log the results.

6. Find and fix issues, then rerun the test.

How Integration Testing Works

Integration testing works by combining or integrating different modules or components of a software and testing their functionality as a group. This means the test is to ensure the interactions between the different modules/units/components work together seamlessly without any error.

Integration Testing Scenario: User Login feature

A web application is composed of different modules for user authentication.

Module A is the UI for the login form, module B is the API endpoint that handles login requests and module C is the database access module.

The login form interacts with the API endpoint, and the API endpoint interacts with the database access module to verify user credentials.

Now, given a valid username and password on the login form, a request is sent to the API endpoint which then queries the database. If these credentials are correct, the API returns success and a dashboard UI is displayed.

A successfully run test means that all the modules work together seamlessly to authenticate a user and load the dashboard without any issues like wrong responses, crashes, or data mismatches.

What does Integration Testing Involve?

Integration testing mainly involves integration of different software components, creating their test cases and running these tests. This is done to check for errors, deb, and then re-run the tests to ensure the integrated modules work together as required. This can be seen in;

• Testing API interactions.

• Database integration checks.

• Network and service communication validation.

• Error handling between modules.

What are the Key Steps in Integration Testing?

When implementing integration testing, there are key steps that have to be followed to ensure perfect test outputs and best practices in software testing. Due to time factors and deadlines, some QA teams tend to ignore these integration testing key steps. They jump directly into application testing without documenting and planning test cases. This can result in missed test cases, bugs in production, and poor quality software.

These key steps that QA teams need to follow are shown below in their respective order.

1. Planning. This involves defining the various modules that need to be integrated, test case documentation, and test plan creation.

2. Environment setup. This step involves installing necessary software and tools for integration testing, setting up the test environment for example mock servers and docker environments.

3. Test execution. After planning and setting up the environment, run the tests. This involves running behavior-driven and data-driven test cases for the system.

4. Evaluation and reporting. After successfully running the tests, found bugs are fixed according to priority and risk score and a report is made.

Maintenance. This step involves documenting some of the steps taken to fix bugs and updating test cases and their status.

What is the Purpose of Integration Testing?

The main purpose of integration testing is to ensure that combined different units/components of a software work and interact perfectly as required. This makes integration testing an important step in the software development life cycle (SDLC).

This purpose is achieved by following the procedures we discussed in the previous section so as to ensure there are no missed test cases, integration bugs arising in production, thus, better quality software products.

What are the Different Types of Integration Testing?

There are different approaches in which QA and Test engineers implement integration testing. The main approaches of integration testing are Big-Bang Integration Testing and Incremental Integration Testing.

Let’s now have a detailed explanation for each of the above approaches.

Big-Bang Integration Testing

This approach of Integration testing involves combining all modules of a system and testing them as one big complete system in one go.

It is used when components are independent and can be tested as individual units.

Pros

• Saves time

• Simple to implement

• Best for smaller systems with few modules.

Cons

• In case something fails, it is hard to isolate/find bugs since all units are tested together at once.

• It’s time consuming in terms of bug fixing incase of test failures.

• There are high chances of some bugs leaking as units are all tested at once.

Incremental Integration Testing

The incremental approach to integration testing is where different modules of the software are integrated and tested step-by-step, one at a time. Each component of the software is integrated and tested, before another component is added. The process is incremental thus the name of this approach.

Pros

• Early catching of bugs due to step by step integration and testing.

• Easy fixing of bugs

Cons

• Time consuming due to the step-by-step combining and testing process for each component.

• Slower and insufficient for larger systems which may need a comprehensive approach.

Incremental integration testing is further divided into Bottom-Up, Top-Down and Mixed Integration Testing.

Let’s have a detailed look into these sub-divisions of incremental integration testing.

Bottom-Up Integration Testing

The bottom-up approach follows that low-level components like databases and individual components are tested first before high-level components. This ensures the foundation of the system is working perfectly before testing the top layers.

Pros

• Ensures a solid foundation of the system

• Manageable and simpler to test low level components first.

Cons

• Slower due to starting with low-level components.

• Later testing of complex interactions makes the testing process harder.

Top-Down Integration Testing

The top-down approach involves integrating and testing system components starting with the high-level components to the low-level ones. This is used when high-level modules depend on low-level modules.

Pros

• Early detection of bugs in high-level components which are critical parts of the software.

Cons

• Requires stubs to implement low level components hence increased complexity.

• Requires more resources for implementing low level component testing.

Mixed Integration Testing

The mixed approach combines both the top-down approach and the bottom-up approach. Here both high and low level components are integrated and tested simultaneously.

Mixed integration testing is also known as hybrid/sandwich integration testing.

Pros

• Provides a full and detailed view of the system due to combination of both top-down and bottom-up approaches

• Testing is balanced as both minor and major modules are tested simultaneously.

• Bugs in both high and low level modules are identified early.

Cons

• It is complex as it combines two approaches unlike the others.

• It is time consuming.

Applications of Integration Testing

Integration testing is crucial and a number of applications in the field of software and computer engineering. Some of the applications of Integration testing can be seen in the following areas;

• Microservices architecture. Integration testing is implemented to ensure APIs communicate correctly.

• Enterprise applications. Integration testing helps validate ERP/CRM integrations.

• Cloud-based systems. Integration testing helps in testing interactions between cloud services.

• IoT Systems. Integration testing is implemented to ensure device-to-server communication.

Difference between Manual Testing and Automated Testing

Now that we have discussed integration testing in detail, take note that software testing can be a manual or automated process. In this section we will look at the differences between manual and automated testing.

But before that, what are they?

Manual testing is a method of testing software where a tester has direct interaction with the software application like an end-user would to find defects without the use of any kind of automation. It involves manually trying out every feature of the software to ensure they behave as expected.

On the other hand, automated testing involves testing software using software tools built specifically for testing the behavior of software applications. These tools control test execution, and compare actual outcomes of an execution with predicted outcomes.

With the advancement in software testing technologies, there has been emergence of tools like Keploy that have made test automation much easier and better.

Keploy streamlines the software testing process by automatically generating tests based on data from your running software application. It provides features like recording and playing test cases, AI-generated test cases, and multi-language support.

Now, let's go ahead and look at the differences between manual testing and automated testing in the table below.

Related blogs and resources

You can go further and look into the resources below to get more insights about integration testing, its counterpart unit testing and their differences.

• Integration testing with Keploy

• What is Unit testing?

• Unit testing vs Integration testing

Conclusion

We have now come to the end of our article, where we explored Integration testing in detail, why its important, its purpose in software development life cycle and the key steps to follow when implementing it. We have also explored the applications of Integration testing, the differences between manual and automated testing and got to know about how Keploy is streamlining test automation.

FAQs

1. Can integration testing be automated?

Yes, tools like Keploy, Postman, and Selenium help automate integration tests.

2. When should integration testing be performed?

After unit testing and before system testing.

3. Is manual integration testing still relevant?

Yes, for exploratory testing, but automated testing is preferred for efficiency.

4.Which type of software testing should you prioritize?

You should prioritize starting with unit tests for core logic, then add integration tests for critical workflows, while ultimately using both together for a robust testing strategy.