In today’s modern world, software hardly operates as a stand alone application. Instead, organizations use different applications to carry out different business functions, and the average company, today, uses roughly 40 different applications to carry out various business processes. For instance, an organization may prefer SAP for finance operations, Workday/ PeopleSoft for Human Resources, Kronos for attendance management, and Salesforce as a CRM. To ensure that seamless communication happens among these applications, organizations must perform robust integration testing.

What is integration testing?
Integration testing refers to the process in which the interface of different applications, modules or components of a software application are tested as a combined group. Integration testing is the second level of the software testing process. And takes place right after unit testing and just before system testing. .

Said another way, integration testing ensures that different applications and technologies are working as intended, together.

Its main objective is to evaluate interfaces between applications and modules and identify any flaws that might occur when they communicate with one another.

Differences between unit testing and integration testing
In unit testing, a single component of an application is tested. It is performed before integration testing using white box testing techniques. White box testing involves examining the internal structure and design of a software application's code to ensure that it is functioning correctly, whereas blackbox testing involves testing a software application without any knowledge of its internal workings, such as its code, algorithms, or data structures.

Instead, the tester relies on functional specifications, user documentation, and other external sources of information to create test cases and perform the testing.

Here are some high level differences between unit testing and integration testing

Unit testing Integration testing
It is a white box testing process It is a black box testing process
It is performed by developers It is performed by testers
Finding defects is easy as each unit is tested individually Finding defects is hard as all modules are tested together
It is always performed first before going through any other testing process It is performed after unit testing and before system testing
Developers are aware of the internal design of the software while testing Testers are not aware of the internal test design of the software
Differences between integration testing and system testing
System testing is the process in which end to end testing of the complete application is carried out.

System testing Integration testing
It ensures that the total build fulfills the business requirements and specifications It ensures all combined units can work together without errors
It is a white box and black box testing or gray box testing It is black box testing
It falls in the acceptance testing class and performs functional and non-functional tests It doesn’t fall in the acceptance testing class and performs functional types of tests
It is level three testing It is level two testing
It helps to identify system errors It identifies majorly interface errors
What are the different types of integration testing

Incremental testing: Refers to when two or more modules are combined logically and tested. The main advantage of incremental testing is that testers can find defects early due to step-by-step examination of integrated applications. Incremental testing can be further classified as

Bottom up testing: This testing type starts from the lowest level module in the architecture. The control flows towards the top of the hierarchy from bottom. Since it can be applied at the early stages, bugs can be fixed straight away. In other words, minimal identification and troubleshooting time is required.

Top down testing: Here, the testing starts with the top module. The testing control flows towards the bottom from the top.

Sandwich testing: Also known as a hybrid integration testing approach, this approach combines both top-down and bottom-up testing approaches. Here, testing is done in both directions - towards higher-level modules (upwards) and towards lower-level modules (downwards) - as the integration process begins at the middle layer (downwards). Since testing control flows in both upward and downward direction, it includes benefits of both top-down and bottom-up approaches and facilitates faster testing of the module’s interfaces.

The downside of sandwich approach is it is complex as it combines two different integration testing approaches and may not be suitable for all types of software applications.
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Big bang testing: Also known as a non-incremental testing type, this type of testing is performed once all the modules are assembled into a complete system. Said another way, all the modules are integrated together and tested as one unit. This type of testing is perfect for smaller systems.

Why you should care about integration testing
Key reasons to conduct integration testing are:

To analyze how disparate applications work together
Organizations prefer different applications to perform different functions, and so integration testing incompatibility issues that may cause errors in a system that disrupt business continuity.

To ensure seamless communication between applications
Applications are often connected with the help of APIs. This type of testing ensures that the data accepted by the API as well as the response generated is correct.

To fix exception handling
To reduce exception handling faults, it is critical to identify the weak points and red flag them before releasing the final release. It will be costly to rectify these errors after the release if they are missed during the initial or developing stage.

Exceptions refer to unexpected events or conditions that disrupt normal flows. Exceptions may be caused by various factors, such as invalid user input, hardware failures, or software bugs.

Integration testing helps solve for exceptions when the individual modules or components of the software application are integrated together.

Integration testing can help ensure that the software application is able to handle exceptions in a consistent and predictable manner, minimizing the impact of errors or unexpected conditions on end-users.

Benefits of integration testing
It ensures that integrated applications or modules work correctly as expected.
It ensures that data transferred via modules to APIs are correct.
It ensures that the application interacts seamlessly with third-party tools and, most importantly, different APIs.
It identifies issues such as broken database schema and cache integration errors.
It reduces the probability of total software failure.
It will help you to check the structural changes when a user moves from one module to the next.
How do you write integration tests?
Here are some general steps for writing integration tests:

Identify the components or systems that need to be tested together.
Determine the inputs and expected outputs for each component or system.
Create test data and set up any necessary infrastructure, such as a test database or mock objects.
Invoke the components or systems being tested and pass in the appropriate inputs.
Verify that the outputs match the expected results.
Clean up any test data or infrastructure that was created.
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When writing test cases, it's important to keep in mind the overall architecture of your application and how the different components interact with each other.

‍Challenges of integration testing
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Lack of standard tools: Testing two different systems developed by two different companies can be very challenging with one standard tool. Finding an automation tool that supports multiple platforms including legacy systems and offers clear visibility and impact of platform changes is a difficult task.

Lack of product support: The basic requirement of continuous integration testing is a test automation tool. Often software development teams incorporate open source or code based test automation tools that are neither well-documented nor easy to operate. Furthermore, these platforms don’t have the ability to automate all the test cases.

Lack of faster feedback loops: Current software development practices involve continuous integration processes for which quick feedback is mandatory. However, QA teams often rely on open source tools that lack robust reporting capabilities. This leads to a delay in action from developers' part, later affecting the quality of the product.

Lack of a real-time dashboard for testing matrices often results in wastage of time. Digging into logs and code-profiler reports to check on a product’s performance is time consuming.

Increased complexity: As the product grows, the scope of testing also. As the test cases increase, it becomes harder to maintain them. This shifts the focus of teams towards maintenance rather than build and test.

Scalability issues: Integration tests are hard to run in parallel. This is due to shared state such as web server & database state. Furthermore, they are slow to run.

Solutions to integration testing challenges
Use an end-to-end platform that supports a range of technology stack including web, app, API, legacy, desktop, and mobile. It enables QA team members to validate critical integration points to keep business risks at bay.
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An end-to-end support for the entire application ecosystem eliminates the need for individual testing platforms for different applications, thereby offering cost benefits to the enterprise.
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Use for a platform that autonomously identifies impacted test scripts and heals them automatically, reducing the burden of test maintenance. .
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Choose a platform that supports scalability and allows test cases to get executed in parallel.
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Select an automation platform that comes powered with robust reporting capabilities so that issues can be reported easily and quickly.