As your program grows, minor errors and edge cases that you didn't expect might build into more significant failures. Errors result in a poor user experience and, as a result, company losses. Testing your code before putting it into the market is one way to avoid fragile programming.
Static Analysis
The basic step in improving the quality of your code is to begin using static analysis tools. The static analysis looks for errors in your code as you write it, but without running it.
Linters examine code for common errors such as unused code and help prevent problems, such as using tabs instead of spaces, and indicate style guide no-nos (or vice versa, depending on your configuration).
Type checking guarantees that the construct you're passing matches what the function was designed to accept.
ESLint for linting and Flow for type checking are two tools that come pre-configured with React Native. TypeScript, a typed language that compiles to plain JavaScript, is another option.
To begin with tests, you must first write testable code. Instead of writing your complete program in a single large file with many lines of code, you break it down into smaller modules that you can test more extensively than if you tested it as a whole. Testable codes are clean and modular.
Start by separating the visible portion of your project—your React components—from your business logic and app state to make it more testable (regardless of whether you use Redux, MobX, or other solutions). Your business logic testing—which shouldn't rely on your React components—can be kept separate from the components themselves, primarily responsible for creating your app's UI!
Writing Tests
Now that you've written testable code, it's time to develop some actual tests. The Jest testing framework is included in the default React Native template. It comes with a setup specific to this environment, so you can get started immediately without messing with the settings and mocks.
Test Structure
Your tests should be concise and should ideally only test one thing. Let's look at an example of a unit test developed in Jest:
it('given a past date, colorForDueDate() returns red', () => {
expect(colorForDueDate('2000-10-20')).toBe('red');
});
The string given to the test function describes the test. Write the description carefully so that it is clear what is being tested. Make every effort to cover the following topics:
Given - some prerequisites.
When - the function you're testing performs some action
Then - the expected result
This is also referred to as AAA (Arrange, Act, Assert).
Jest has a describe function that can help you structure your tests. To group all tests that correspond to the same feature, use describe. Other useful functions are beforeEach and beforeAll, which you can use to set up the items you're testing. More information can be found in the Jest api reference.
If your test includes a lot of stages or expectations, you should usually break it up into smaller tests.
Make sure that your tests are independent of each other.
Each test in your suite must be self-contained and run without the need to run any other tests first.
If you run all of your tests simultaneously, the output of the first one should not affect the output of the second.
Note:As developers, we like it when our code runs well and does not crash. When it comes to tests, this is not the case. Considering a failed test is a good thing! When a test fails, it usually indicates that something is wrong. This allows the developers to address the issue before it affects the users.
Unit tests
Unit Testing is a level of testing at which individual software components are tested. We do it to make sure that each component functions properly. A component is the smallest unit of software that can be tested.
Mocking
When tested objects contain external dependencies, it's sometimes necessary to "mock them out." When you "mock" a dependency in your code, you replace it with your implementation.
Unit Testing In React Native Applications
A variety of tools can be used to test a React Native application, including the following:
WebDriver: This is an open-source Node.js testing tool that can be used to test React Native applications.
Nightmare: This automates test processes in the browser. "The idea is to expose a few simple methods that simulate user actions (such as goto, type, and click), with an API that seems synchronous for each block of scripting, rather than highly nested callbacks,"
Jest: This is one of the most widely used testing libraries. It, like React, was developed by Facebook and was created to provide a "zero-configuration" setup for the best efficiency.
Mocha:Mocha is a well-known testing library for React and React Native applications. It has become a popular testing tool among developers because of how simple it is to set up and use and how fast it is.
Jasmine: Jasmine is a behaviour-driven development framework for testing JavaScript code.
Frequently Asked Questions
What is React Native used for?
React Native combines the best features of native programming with React, a top-of-the-line JavaScript toolkit for creating user interfaces. You can use React Native in your existing Android and iOS projects right now or start from scratch and build a brand new app.
What are the different types of testing in React?
When we talk about front-end testing in React, we're talking about making claims about how our React app renders and reacts to user input. Unit, functional, and integration testing are three different software testing paradigms.
What is an API, and what do you mean by API integration?
An API is an interface that allows multiple applications to exchange data. API integration means using APIs to fetch data from a remote URL and using it in your app as per your business requirement.
Conclusion
In this article, we learned about different types of testing we can perform in React Native applications. Starting from learning the best practices to write a testable code, we looked at some of the tools that can be used to test a React Native application.
Want to learn more about coding practices in React Native? Don’t Worry; Coding Ninjas has you covered. To learn, see React Native Debugging.
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