When building a software system, testing is an essential part of the software development workflow. As software developers, we all want to write programs that work as expected. The program is bug-free, and testing can help achieve this goal.

This article discusses a testing approach called unit testing. What are unit tests? How should it be implemented? What are the advantages and limitations of single testing?

What are unit tests

The goal of unit testing is to isolate each part of the program and show that each part works as expected. Unit tests are automated tests written and run by software developers to ensure that a part of the application, called a unit, works as expected.

A unit is the smallest piece of code that can be logically isolated in a system. This can be a single function, method, procedure, module, class, or object. Typically, a unit has several inputs and one output. Unit testing is done by software developers during the development (coding phase) of the application.

Only when the parts work well can the whole system work well. By writing tests for the smallest testable unit, the software developer builds confidence that the entire system will work as expected. Once a software developer writes a unit test, they can run it on their local machine to check that the test passes. They can also run all the other pre-existing tests to check that they still pass.

Unit testing framework

Software developers often use unit testing frameworks to develop automated test cases for unit testing. A unit testing framework is a software tool that supports writing and running unit tests, including the foundation for building tests and the ability to execute tests and report results. Unit testing frameworks with the most popular programming languages.

During test case execution, the framework records failure of any standard tests and reports them in the summary. Depending on the severity of the failure, the framework may stop subsequent testing.

Unit tests can also be set up to be executed on each new build before the code is released to staging or production. In this way, software developers can ensure that only code that passes all unit tests will enter the real-time environment. If any unit tests fail during the build process, the software developer can fix the problem before trying to release it again.

Unit Test Examples

Here is a very simple example of how unit tests work. We have a simple add function that takes two numbers as arguments and returns the sum of the two numbers. I’m using Spock, the recently learned (and actually reviewed) Groovy unit testing framework, to demonstrate this. If you’re interested, take a look at the old article:

  • Spock is configured in Maven and Gradle
  • Groovy unit testing framework Spock basic functionality Demo
  • Groovy unit testing framework Spock data driven Demo
  • Life is short? Try Groovy for unit testing
  • Initial exploration of Spock 2.0 M1
  • Unit testing frameworks spock and Mockito applications
  • Groovy dynamically adds methods and properties and Spock tests
    static int add(int i, int j) {
        return i + j
    }
Copy the code

Our very simple first unit test of the Add function is as follows.

    def "Test add method"() {
        given: "Have Fun ~ Tester!"

        expect:
        sum == add(i, j)

        where:
        sum | i  | j
        2   | 1  | 1
        1   | -1 | 2
        0   | 0  | 0
    }
Copy the code

We can then add more unit tests to the add function and use other sample inputs to override different cases, such as negative numbers or invalid input parameters, to check that errors are handled correctly. This is a very simple example, but it shows how unit testing works in practice.

Benefits of unit testing

Unit testing is a method of software testing in which individual units, components, or modules of software are tested to determine whether they are fit for use. Therefore, it has many benefits. As software systems evolve, software developers benefit more from unit testing. If appropriate unit testing is done early in development, it will ultimately save software developers time and money.

Unit tests find problems early in the development cycle. This includes errors implemented by software developers. The cost of finding bugs before you start coding or when you first write code is much lower than the cost of detecting, identifying, and correcting bugs later.

Unit testing helps software developers create better software designs. If written poorly, code may be impossible or difficult to unit test, so unit testing can force software developers to build functionality and objects in a better way. The process of writing a complete set of tests forces software developers to carefully consider input, output, and error conditions to more clearly define the behavior required by the unit.

Because of the modular nature of unit testing, software developers can test various parts of a software system without waiting for other parts to complete. This will help software developers create their software in small agile increments.

Unit testing allows software developers to easily refactor code or upgrade system libraries at a later date and ensure that existing code still works. Any changes made by software developers that cause existing unit tests to fail can be quickly identified and resolved. Unit tests detect changes that might break existing working code.

Unit tests create system documentation as a positive side effect. Software developers who want to understand what a unit provides and how to use it can look at unit tests to get a basic understanding of unit interfaces (apis).

Unit testing restrictions

While unit testing has many benefits, it also has some limitations.

Unit tests do not catch every error in a software system. Unless it is a very simple system, it is difficult to evaluate every execution path in a software system. Unit tests are limited to testing the functionality of the unit itself. It does not catch other errors, such as integration errors or performance errors.

Setting up unit tests can be difficult if the core function of the unit under test is to interact with things outside the system. External things such as databases, file systems, or external apis can be challenging when unit testing. Software developers may have to simulate interactions with external parties, which can be challenging and not exhaustive as testing.

Last

Writing unit tests as part of system development often feels expensive and slow. More code needs to be written, and writing good unit tests takes time and effort. A common mistake development teams make is to skip unit tests.

As most software systems grow, they will benefit from extensive unit test coverage. Unit testing makes it easier to add new functionality, refactor existing functionality, and understand existing individual components of a system. Adding unit tests early will ultimately save software developers time and increase productivity.

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