Change Your Mind About Unit VS Integration Testing To Support Your Product’s Progress

Reading Time: 14 minutes

Software complexity is going up. User-centricity is taking over. And businesses get lost in all the tiny and mammoth tasks. We get so caught up in the bullet-speed progression of technologies that we forget something very simple:

Fundamentals are still fundamentals. Pay them due attention and they’ll bless you with easier and trust-worthy development.

That’s why today, we’ll honor unit vs integration testing. They’ve become so common that we rarely talk about them now. What’s more, we don’t treat them as something critical. And we need to change that. Because this duo of “basic” tests will be the backbone of your entire project.

What Is Unit Testing?

Unit testing checks how a piece (unit) of code works. Briefly, you take the smallest testable component and run it to see if it does what it should.

In simple terms, a unit test could be equated to you examining a screw. Does it have imperfections? Is it easy to use? Will it hold the shelf in place? It’s a tiny element of the bigger structure that nonetheless decides how stable the build is.

Now, the terms in the IT space are often blurry. And there are different approaches to defining this “unit of code”. But generally, it’s underpinned by:

• Functions – self-contained blocks of code that perform a specific task.
• Methods – the behavior or actions that objects of that class can perform.
• Classes – the properties (attributes) and behaviors (methods) that objects of that class have.

So, when you find yourself questioning what a unit test should include, consider these traits:

• The code should be modular, composed of discrete, self-contained units with well-defined responsibilities.
• It should hide implementation details and expose only necessary interfaces or APIs for interaction with other units of code (encapsulation).
• Each unit of code should be independent of external factors.
• The behavior of the code should be deterministic, always producing the same output.
• The code should exhibit low coupling, minimizing dependencies between units.
• It should be highly cohesive, with a clear and focused purpose and related functionality grouped together.
• The code should be easy to refactor without breaking existing unit tests.

Units that don’t fit within these qualities should be eliminated from the testing suite. You don’t want to waste time on something that can be tested on other layers.

Unit Testing Examples

Now that we’re clear on what unit tests are, let’s review some scenarios to see how these checks look in practice.

#1 – Arithmetic Operations

Scenario: Testing a simple arithmetic function, such as addition or multiplication.
Example: Test that addition of 2 and 3 returns 5.
Expected outcome: The function should return the correct sum of the two numbers.

# 2 – Data Validation

Scenario: Testing a function that validates user input or data format.
Example: Test that validate_email (“example@example.com”) returns True.
Expected outcome: The function should correctly validate the format of the email address.

#3 – Error Handling

Scenario: Testing error handling in a function.
Example: Test that a function raises an exception when offered invalid input.
Expected outcome: The function should raise an appropriate exception when given invalid input.

#4 – Boundary Conditions

Scenario: Testing edge cases or boundary conditions of a function.
Example: Test that a sorting function correctly handles an empty list or a list with a single element.
Expected outcome: The function should handle these special cases without errors and produce the expected output.

#5 – Database Interaction

Scenario: Testing a function that interacts with a database, such as retrieving data or performing CRUD (Create, Read, Update, Delete) operations.
Example: Test that a function that retrieves user information from a database returns the correct user data.
Expected outcome: The function should correctly retrieve the user data from the database and return it as expected.

What Does Unit Testing Cover?

So, we know that unit tests verify individual components in a system. Logically, you would think that for a better, cleaner codebase, you’d want to achieve 100% coverage. But you shouldn’t. While unit tests are small, simple, and quick, if you have millions of them – that isn’t sustainable.

Developers could spend their time checking these tiny components. And that would minimize the likelihood of complex issues popping up later. Yet, realistically, it’s not practical or really needed. Because when you have an ocean of unit tests to deal with, you don’t have time for other tasks.

Thus, the best approach to utilizing unit testing to your advantage is to focus on:

• High-priority or critical elements.
• Functions users rely on continuously.
• Code that’s frequently accessed.

And in terms of what unit testing does, well, there are a couple of things.

• Unit tests verify the behavior of a unit of code against specific inputs.
• They cover various edge cases and boundary conditions.
• Unit testing verifies that error handling mechanisms in the unit function correctly.
• Although less common, some tests may evaluate the performance characteristics of a unit.
• Unit tests aim to exercise as much of the codebase as possible to identify issues.
• They serve as a safety net during refactoring, ensuring that modifications to the codebase don’t break existing functionality.
• Well-written unit tests can also serve as a form of documentation. They provide insight into how a unit of code is expected to behave and how it should be used.

Overall, unit testing is a speedy approach to assessing your code’s stability on the unit level.

Why Is Unit Testing Important?

If we ask our good old friend – the Testing Pyramid – why unit testing is considered irreplaceable, it’ll tell us three things:

1. These tests are easy and quick to run. So you can check a lot with minimal effort.
2. Units form the backbone of the software. And a well-inspected base translates to better structures on top.
3. Your approach to unit testing, say TDD, can encourage superior quality from the start.

Every iteration of the Testing Pyramid (and there’re about a dozen of them) never skips unit testing. And each of them always places these tests at the foundational level. As it indeed lays the foundation for your product’s quality.

And now, a few more words on the powers of unit testing.

Why the Two-Decade-Old Testing Pyramid Still Works

Detecting Bugs Early

Unit testing validates the base layer of the software. The cleaner it is, the less the risk of serious problems appearing later. By testing individual units, developers can identify and fix issues before they propagate to other parts of the system.

Improving Maintainability

When developers modify code, they can run the associated unit tests to ensure the alterations didn’t break anything. This promotes code maintainability and reduces the risk of introducing new bugs during maintenance or refactoring.

Simplifying Refactoring

Speaking of the latter, unit testing provides confidence when refactoring code. Developers can be sure that if the unit tests pass, the behavior of the code remains unchanged. This encourages code improvements and redesigns without fear of introducing bugs.

Facilitating Regression

Unit tests can also be a form of regression testing. Devs can run them frequently to catch regressions promptly. This way, they easily secure operating functions after modifications.

Refining Design

Writing unit tests often leads to better-designed code. To make code testable, developers often need to decouple components, which can result in more modular, reusable, and maintainable code.

Supporting Continuous Integration/Deployment (CI/CD)

Unit tests are a cornerstone of CI/CD pipelines. And here, it’s a great idea to couple unit testing with automated testing services. They help ensure that code changes are thoroughly tested before deployment. Devs don’t spend too much time on running tests. And you have increased trust in your product’s quality.

Reducing Costs

Unit testing can also be your expense saver. It helps reduce the overall cost of software development by detecting issues early when they are cheaper to fix.

Advancing Code Confidence

Passing unit tests indicates that the code behaves as expected. In turn, this reduces uncertainties and risks associated with software development projects. And devs, QA engineers, and stakeholders can be more confident in the codebase’s quality.

An Effective Approach to Selecting Test Cases for Automation

When to Run Unit Testing?

From most resources, you’ll get the idea that unit testing is run very early in the SLDC. It’s usually the first type of testing to touch the system. But in reality, unit tests’ timing can vary.

Based on the development process and project needs, unit testing can quantum jump all around. Some say it should be executed once and forgotten. Others insist on using it with every commit.

So, let’s summarize. Unit testing can happen:

• During development for neat code and bug-free software levels.
• After changes to not present regressions.
• Before integrating new code changes into the main codebase.
• As part of the CI pipeline to automate the testing process.
• Before deployment to ensure the code meets the required quality standards.
• After environment changes to secure correct behavior of existing functionalities.
• As needed (e.g., after major refactorings, bug fixing, feature additions) to maintain code quality.

When to run unit testing is quite personalized. And you should always tailor it to your project specifics. But consider a piece of advice from us as a QA company with a decade of experience – perform these tests as the development goes and do so frequently.

You’ll benefit from refined code and a swift feedback loop.

Reviewing Your Testing Strategy – How to Do It Right?

Who Runs Unit Testing?

With QA services, there are always many answers to who does what. But it shouldn’t be the main concern. Instead, focus on how a person does what they should.

For example, you wouldn’t want a dev performing E2E testing. It would be quite difficult and time-consuming for them. Plus, a professional QA engineer would do a better job simply because they’re trained for it.

And you won’t ask a QA specialist to design a feature for, say, a medical device from scratch. You’d be met with a side eye, that’s for sure.

Unit testing is a bit more straightforward in this context. It’s primarily conducted by software developers. Because they can test as they write or write before they test. Also, unit tests are quite simple and don’t need deep expertise to get the results you want.

What Is Integration Testing?

Unlike unit testing, which focuses on small code bits, integration testing combines a few of them. It gathers related units into modules to see how they collaborate.

Remember our example with unit tests acting like screws? With the same analogy, integration tests would be you checking a compartment of a closet you’re making. Instead of looking at its basic elements, you now assess how well a section of the structure is made.

• Maybe the screws you added later created a curvature in the shelf?
• Perhaps some of them fell off?
• Or you find that one of them isn’t needed at all?

And thus, integration testing means combining software components to inspect how they work together.

Integration Tests Examples

Here are a few examples of what integration tests would do for different modules.

Authentication Integration

Scenario: Testing the integration between a user authentication module and a database.
Example: Verify that a user can successfully log in after their credentials are authenticated against the database.
Expected outcome: The user authentication module should grant access upon successful validation of user credentials stored in the database.

Messaging Integration

Scenario: Verifying the integration of a messaging service with a notification system.
Example: Test that sending a message through the messaging service triggers a notification to the recipient.
Expected outcome: Upon message delivery, the notification system should promptly notify the recipient.

Billing Integration

Scenario: Testing the integration between a billing system and a payment gateway.
Example: Verify that completing a purchase transaction through the billing system successfully processes the payment via the payment gateway.
Expected outcome: After initiating a purchase, the billing system should transfer payment details to the payment gateway.

File Storage Integration

Scenario: Verifying the integration of a file storage service with a file-sharing module.
Example: Test that uploading a file to the storage service enables sharing it through the file-sharing module.
Expected outcome: Upon uploading a file, the file-sharing module should provide a shareable link.

Scheduling Integration

Scenario: Testing the integration between a scheduling module and a calendar application.
Example: Verify that creating an appointment in the scheduling module reflects accurately in the user’s calendar within the calendar application.
Expected outcome: Upon scheduling an appointment, the calendar application should promptly update to display the newly added event.

Unit Testing VS Integration Testing VS Functional Testing

At this point, we should clear something right away. To avoid any confusion, we need to chat about the ever-present “unit testing vs functional testing vs integration testing” conundrum.

Let’s review what functional testing is.

It evaluates functionality by testing individual features or functions against specified requirements.

Now, isn’t it kinda what unit testing and integration testing do?

In a way.

First, unit and integration tests fall under functional testing services. Because each of them checks how well something works.

Second, functional testing in a high-level assessment. It investigates software features as a whole.

And third, functional tests look at the functional requirements and behavior of the software from an end-user perspective. So, they don’t consider internal code structures. These tests are typically black-box, centering on user expectations (not technicalities).

To not get stuck in the “unit testing vs integration testing vs functional testing” obscurity, remember this:

• Functional testing is an umbrella term.
• It branches out into unit and integration tests, among others.
• And it’s divided so to check various layers of a product.

Having established that, now, we continue with “dissecting” integration testing.

What Does Integration Testing Cover?

Since integration tests are about connections between your software, they focus on the communication between its parts.

• Verifying the communication between different software modules or subsystems (APIs, database connections, and messaging protocols).
• Ensuring that data flows correctly between integrated components.
• Testing E2E functionality across multiple integrated components, prioritizing users’ POV.
• Assessing how changes in one element affect other integrations.
• Securing proper dependency management.
• Validating error handling mechanisms and recovery procedures.
• Evaluating system performance and scalability under integrated conditions.
• Verifying compatibility with external systems, platforms, or environments.

Curiously, integration testing occupies the middle level within the Testing Pyramid. So, it confirms your product’s adequate connections. And acts as a checkpoint you need to pass before moving on to other tests.

Why Is Integration Testing Important?

In one of our previous articles, we’ve touched upon the subject of integration abandonment. These tests usually take place after unit and before system testing. The logical assumption would be to skip this “middle man”. It’s extra time and money, after all.

But with QA services, disregarding something is an automatic loss. You’ll find odd issues appearing seemingly out of nowhere. Systems producing bogus outputs. Your teams being overwhelmed by post-production work. And your product suffering from degraded quality.

For a more in-depth look at the remarkable perks of integration testing, check out the link below. But, for now, let’s summarize the main points.

Don’t Take Software Integration Testing for Granted – Run It Like This

Detecting Interface Issues

Integration testing helps identify issues related to the interactions between software components. By testing how they communicate and exchange data, you uncover potential communication failures, protocol mismatches, or data transfer errors.

Verifying System Behavior

Integration testing validates the behavior of the system as a whole. It ensures that the integrated units function correctly together, confirming that the system performs as expected.

Identifying Integration Bugs Early

By locating integration issues early, you prevent them from escalating into more significant problems later. In turn, you save time and resources by nipping the bugs in the bud (that’s a good tongue twister).

Ensuring Interoperability

Integration testing helps confirm that systems can communicate without compatibility issues. Thus, you can be sure that your product exchanges data productively, regardless of the technology stack or platforms involved.

Mitigating Risks

Through integration tests, you reduce the risk of system failures or malfunctions. By uncovering issues before deployment, you advance its reliability, stability, and performance.

Improving System Quality

By thoroughly testing the integration of software components, you refine the overall quality of your project. This secures fulfilled functional requirements and delivers a positive user experience.

When to Run Integration Testing?

Integration testing goes hand in hand with unit and system tests. But, as always, that doesn’t necessarily mean that it’s the only available slot for executing it.

• In agile or iterative development methodologies, integration testing is conducted incrementally as new features are developed.
• In environments practicing CI, integration tests are automated and run frequently. They’re typically triggered by code commits to the version control system.
• Integration tests are also executed during the integration of larger system components or subsystems.
• They’re typically completed before user acceptance testing to ensure the system’s ready for user validation.
• And these tests may be performed after regression testing to ensure cohesion.

Generally, you want to run integration testing throughout the development process. As you never know what might go wrong. But if something goes wrong too often, well, you should reevaluate your QA resources. Because the success of your integration testing services heavily depends on the expertise of the team.

Who Runs Integration Testing?

In this round of unit vs integration testing, the latter wins. Because, while it can also be performed by multiple agents, only specialists with precise skills can do it right. So, the pool of potential executors goes down.

QA engineers carry out quality reviews and audits to identify areas for improvement in integration testing practices.

Test automation engineers develop and maintain automated test scripts and frameworks to streamline the execution of integration tests.

Developers collaborate with QA experts to understand test requirements, review test cases, and address defects identified during integration testing.

Project managers coordinate resources, prioritize testing tasks, and communicate testing progress to stakeholders. They participate in test planning meetings, reviews, and retrospectives to optimize integration testing processes.

If we simplify the answer to who runs unit testing vs system integration testing, we get this:

• Developers perform unit tests (and QA engineers can help improve it).
• QA experts execute integration tests (and developers can help improve it).

The rest of the professionals we’ve mentioned definitely have a strong effect on how integration vs unit testing is done. But they rarely participate in running it.

Unit Testing VS Integration Testing: Comparisons & Contrasts

Here, you might ask: “Why exactly are we comparing unit vs integration testing? Why is it so critical to grasp the difference between them?”. The answer is – the tangle that comes from a multitude of online sources. If this is not your first article mentioning “integration testing vs unit testing”, then you’ve probably come across something like:

• “When to use integration testing?”
• “Should you run both unit testing and integration testing?”
• “Which one to pick – unit testing vs integration testing?”

All this might give you the idea that you can omit one of them.

• Unit tests are tiny, so they don’t decide much.
• Integration tests are the intermediary between unit and system testing, so you don’t really need to bother much with them.

These ideas are what will get your product in trouble. Because these testing types serve precise purposes within your product (as you already know). Alas, to dispel any illusion an oddly phrased argument on the web might evoke in you, let’s juxtapose the two. And we’ll be able to make sure you get the best for your project.

Unit Testing VS Integration Testing: Key Similarities

The similarities between integration testing and unit testing can be attributed to their shared goals. They both help secure polished product quality. And thus, they have complementary roles in the testing process.

Unit and integration tests are meant to support each other. Not divide people on whether or not either of them is actually needed.

• Both unit testing and integration testing can be automated (while manual testing services can also be beneficial for the latter).
• They typically occur in controlled testing environments rather than in production.
• Similar testing tools and frameworks can be used for them.
• In unit testing and integration testing, developers define test cases that include assertions or validations to verify expected system behavior.
• Both types of testing provide feedback to developers regarding code correctness and quality.
• Unit tests and integration tests are rerun as part of the regression testing process.
• The two require careful management of dependencies.
• Developers may use similar techniques and tools to diagnose and resolve issues uncovered by unit tests and integration tests.

Unit Testing VS Integration Testing: Key Differences

And as for divergences of unit vs integration testing, it’s quite simple. The duo aims to check something from different perspectives. From a single brush stroke to the bigger picture – it’s just easier to test your product incrementally.

That’s what unit and integration tests do for you. They simplify something challenging yet beyond valuable – software testing services.

Unit tests:

• Focus on individual software components in isolation.
• Are designed to be independent of external dependencies.
• Are fine-grained and focus on testing specific functionalities within individual units.
• Are usually executed in isolation within the development environment or on the developer’s local machine.
• Provide fast feedback by quickly identifying defects or regressions within singular elements.

Integration tests:

• Verify the interaction between components of the software.
• Explicitly test the interactions and dependencies between different units.
• Are coarse-grained and focus on testing the system as a whole, including how different modules interact and collaborate.
• Are often executed in a more complex environment that closely resembles production.
• Provide feedback on how well different components integrate and work together as a system.

We’ll summarize the core distinctions via a table. And you can save it as a little helper note for your team.

Unit Testing	Integration Testing
Tests individual units or components in isolation.	Tests interactions and integration between multiple units or components.
Fine-grained, focusing on specific functionalities within units.	Coarse-grained, focusing on testing broader scenarios involving multiple units.
Dependencies are typically mocked or stubbed to isolate the unit under test.	Dependencies between units are explicitly tested. Real or simulated dependencies may be used.
Often executed within the development environment or on the developer’s local machine.	May require a more complex environment resembling the production environment, including interconnected components, databases, and external services.
Provides fast feedback on the correctness of individual units.	Provides feedback on how well different units integrate and work together as a system.
Tests are isolated and do not require the presence of other units or components.	Tests may require the presence of other units or components to validate integration and interactions.
Focuses on internal logic, behavior, and functionality of individual units.	Focuses on collaboration and interaction between different units to achieve system-level functionality.
Typically has faster execution due to the smaller scope and fewer dependencies.	May be slower to execute due to the broader scope and dependencies between units.
Easy to pinpoint where an issue occurred.	Needs some analysis to locate the issue.
Is performed by developers.	Is performed by QA engineers.

To Sum Up

Common sense isn’t as common as you might think. And many get charmed by the promises of never-seen-before perks of new tech or methodologies. But with an unstable base, anything you add to it later will be just as insecure. So, before refining your product with visionary approaches – make sure you have a foundation to support them.

Do unit and integration testing right. Do it with QA Madness.