Unit Testing vs Integration Testing

Whether you’re working on a simple web application or building out an extensive enterprise system, testing is a key part of the development lifecycle.

Of course, figuring out which testing methods and review tools to use and when to make the most of our tests is a critical aspect.

Of the many testing methods we can use, unit testing and integration testing are two of the most common. If you’re interested in learning more about the pros, cons, use cases, and best practices for each, keep reading.

What is Unit Testing?

Individual units represent the functions, subroutines, properties, or methods. The purpose of unit testing is to test one of these isolated elements individually.

It's important to note that the term “isolated” is actually a key part of the definition of unit testing. 

Michael Feathers, author of "Working Effectively with Legacy Code,” explains that if a unit test interacts with a file system, talks to a database, or can’t be run alongside any other test, it’s not truly a unit test.

Unit testing gained traction long before serverless environments. In fact, it reaches back to the 1950s. Still, modern unit testing is extremely valuable, which is why frameworks like JUnit and updated testing tools incorporate this technique.

The reason why it’s one of the most prevalent types of testing is simple: It’s flexible. A “unit” can be just about anything you want.

It generally represents the smallest logical piece you can break a system down into. This could be a class, method, or individual line of code.

The smaller our unit is, the better our unit test will be. This is because testing a small piece of code gives you a much more detailed look at how it’s performing.

In other words, this testing technique, while targeted, is extremely practical and actionable. Small unit tests run rapidly fast, giving us the option to test thousands of units in a second.

Pros of unit testing

• Unit testing is a key part of the development process.
• Given how simple they are, you can easily set up automated tests.
• Alongside test automation, the small size makes it possible to run thousands of tests in a second.

Cons of unit testing

• Testing individual units of code is good for verifying individual functions, but test coverage is limited and may not reveal dependencies.
• Unit testing isn’t ideal when you need to test a whole application or gain performance insights into your overall system.

What is Integration Testing?

Integration testing is a testing method that requires us to logically integrate various software modules and test them as a group.

Integration testing helps expose issues in module interaction, which tend to be relatively common because modules aren't all developed by the same individuals or teams.

In addition to ensuring that modules work harmoniously together, integration testing also assesses issues with external hardware interfaces and database interfaces.

Additionally, integration testing may be necessary if the project requirements change and unit testing isn’t consistently performed when those changes are implemented.

With the concept of integration testing in mind, it’s worth noting that testers have options when it comes to performing an integration test.

A few of the most popular approaches include the “big bang” approach or the incremental approach, which is further broken down into the bottom-up, top-down, or sandwich approach.

Pros

• You can easily test different modules with ease.
• You can apply it in various phases of the software development process.
• Different approaches are available depending on your test case.

Cons

• Top-down integration testing needs too many test stubs.
• Bottom-up integration testing doesn’t test critical components until late stage development.
• The big bang approach to integration testing can be disorganized and doesn’t allow for isolation.

Best Practices of Unit Testing

When done right, unit testing can help us fix bugs early, improve code quality, and even act as documentation as teams carry out routine system testing.

However, it’s easy to go astray when planning unit tests. If we fail to follow the best practices of unit testing, we'll find it hard to realize any benefits from our efforts and our software application could suffer as a result.

So, what do you need to do to get ready for effective unit tests?

• Tests should be fast, which means making them as simple and as small as possible.
• There should be no dependencies on external resources or other tests. If there are, you’re not running a true unit test.
• Tests should be readable, which promotes simplicity and ease of use. Complicated tests won’t be readily used by developers.
• Use variables or constants to document the values used in your tests.
• The result of a unit test should be either pass or fail.
• Tests should be deterministic, which means the outcome only changes if the production code it targets changes.

Best Practices of Integration Testing

Integration testing is another valuable testing method and it’s a step up beyond unit testing, which means it’s the first stage of testing where we’ll begin to explore how the entire system works together.

However, one of the key differences between unit and integration testing is that the latter dives into a much larger codebase, introducing more room for errors that you might miss.

Following these best practices is key to getting the most out of your tests:

• Analyze each of the approaches you can take to integration testing before deciding how to put the test together.
• Integration testing should only begin once all modules you’re testing have passed all unit tests.
• Integration tests should be made to break things, meaning you should keep testing until something fails.
• Once something fails, determine what needs to be modified and utilize unit testing where necessary.
• Do not let integration tests be the “final stage” in your testing plan. Functional testing requires multiple layers of review beyond unit and integration testing.

Which testing method should you use?

When it comes to the various types of software testing, it's tempting to look at these two testing methods and figure out which one is best suited for our team or development model.

However, one type of testing simply won’t cut it. End-to-end testing is one of the key prerequisites before releasing any system or software.

After all, the cost of bug fixes and security problems after release is substantially higher than fixing them as we go along.

With this in mind, it’s not a question of which testing method we should use, but when we should use them. In other words, use both — keeping in mind the ideal use case for each:

• Unit testing is ideal for test-driven development, documenting code, and checking our work as we go.
• Integration testing is one step above unit testing in the testing pyramid and it’s ideal for reviewing external dependencies and issues with module specifications.

Ultimately, when it comes to optimizing our systems and workflows, there are many aspects to consider beyond unit testing vs integration testing.

If you're interested in working with a team of experts to help you develop an efficient and effective testing strategy, Adservio can help. Contact us to learn more.