10 Jasmine Best Practices

Jasmine is a popular JavaScript testing framework that helps developers write better code and ensure that their applications are functioning as expected. It’s easy to get started with Jasmine, but it can be difficult to know what best practices to follow.

In this article, we’ll discuss 10 best practices for using Jasmine. We’ll cover topics like organizing your tests, writing clear tests, and more. By following these best practices, you can ensure that your tests are accurate, reliable, and maintainable.

1. Use the beforeAll and afterAll methods to set up and tear down test suites

The beforeAll and afterAll methods are used to set up and tear down test suites, respectively. The beforeAll method is called once before all of the specs in a suite have been run, while the afterAll method is called once after all of the specs in a suite have been run. This allows developers to perform setup and teardown operations that need to be done only once for an entire suite of tests.

For example, if you’re testing a web application, you may want to open a browser window before running any of your tests, and close it after all of them have finished. You can do this by using the beforeAll and afterAll methods to open the browser window at the beginning of the suite, and then close it when the suite has completed. This ensures that each spec in the suite runs with the same environment, which helps ensure consistent results.

Using the beforeAll and afterAll methods also makes it easier to maintain your test suites. If you ever need to add or remove a spec from a suite, you don’t have to worry about setting up or tearing down the environment again – the beforeAll and afterAll methods will take care of that for you. This saves time and effort, and makes it much easier to keep your test suites organized and up-to-date.

2. Use spies for mock functions instead of stubs when possible

Spies are more versatile than stubs because they can be used to both spy on existing functions and create new ones. This means that spies can be used to test the behavior of a function without actually calling it, which is useful for testing asynchronous code or when you don’t want to call an expensive operation. Spies also allow you to check if a function was called with certain arguments, how many times it was called, and what values were returned.

Using spies instead of stubs also allows you to keep your tests DRY (Don’t Repeat Yourself). Instead of having to write out the same stubbed function multiple times in different tests, you can just use one spy and configure it differently depending on the test. This makes it easier to maintain your tests since you only have to update the spy once if something changes.

When using spies, it’s important to remember to reset them after each test so that they don’t interfere with other tests. You can do this by calling the Jasmine reset() method before each test. Additionally, you should make sure to set expectations on the spy before calling the tested function, otherwise the test will pass even if the function doesn’t behave as expected.

3. Don’t use global variables in tests

Using global variables in tests can lead to unexpected behavior and results. This is because the same variable name could be used in different test suites, leading to confusion about which value should be expected when running a particular suite. Additionally, if the same variable is used across multiple tests, it can cause unintended side effects that are difficult to debug. For example, if one test changes the value of a global variable, this change will persist for all subsequent tests, even if they don’t expect or need the new value.

To avoid these issues, Jasmine provides an alternative approach called dependency injection. Dependency injection allows developers to pass values into their tests as parameters instead of relying on global variables. This makes tests more self-contained and easier to understand, since each test only needs to know what values it expects to receive from its dependencies. It also helps ensure that tests remain isolated from each other, since any changes made to a parameter’s value won’t affect other tests.

Furthermore, using dependency injection encourages better code organization by making it clear which parts of the application are being tested. By explicitly passing in the necessary data, developers can easily identify which components are being tested and how they interact with each other. This makes it much easier to maintain and refactor tests over time.

4. Use the setup and teardown method to prepare data for each test

The setup method is used to create a common environment for all tests in the suite. This means that any variables, objects, or functions declared within the setup will be available to each test in the suite. This allows you to avoid repeating code and makes it easier to maintain your tests.

The teardown method is used to clean up after each test has been run. This ensures that no data from one test affects another test, which can lead to unexpected results. It also helps keep your tests organized by ensuring that each test starts with a clean slate.

Using both the setup and teardown methods together is an effective way to ensure that each test runs independently of the others. By setting up a common environment before running each test and then cleaning up afterwards, you can make sure that each test is isolated from the rest and that the results are reliable.

5. Use describe blocks to group related specs together

Describe blocks are used to group related specs together, and they provide a way to organize tests into logical sections. This makes it easier for developers to read the test code and understand what is being tested. It also helps with debugging by providing more context when an error occurs.

Using describe blocks can also help reduce duplication in your tests. By grouping similar specs together, you can use beforeEach() and afterEach() functions to set up and tear down common fixtures that will be shared across all of the specs within the block. This reduces the amount of code needed to write each individual spec, making them simpler and easier to maintain.

Describe blocks also allow you to nest other describe blocks inside of them. This allows you to further break down your tests into smaller, more manageable chunks. For example, if you have a complex application with many different components, you could create a separate describe block for each component and then nest additional describe blocks within those for specific features or functionality. This makes it much easier to find and debug any issues that may arise.

6. Make sure your expectations are clear and concise

When writing tests, it’s important to be as specific and explicit as possible. This helps ensure that the test is actually testing what you think it is, and not something else. If expectations are too vague or broad, then your test may pass even if the code isn’t doing what you expect it to do.

To make sure expectations are clear and concise, start by breaking down the behavior of the code into small, individual pieces. For example, instead of expecting a function to return an array with all the elements in order, break it down into two separate expectations: one for returning an array, and another for making sure the elements are in order. This way, if either expectation fails, you know exactly which part of the code needs to be fixed.

It’s also important to use descriptive language when writing expectations. Instead of using generic words like “should” or “must,” try to be more specific about what you’re expecting. For instance, instead of saying “the function should return an array,” say “the function must return an array containing all the elements in the correct order.” This makes it easier to understand what the test is checking for, and can help prevent any confusion or misunderstandings.

Additionally, Jasmine provides some helpful matchers that can be used to make expectations clearer. These matchers allow you to check for certain conditions without having to write out long, complicated assertions. For example, instead of writing out an assertion to check if an element exists in an array, you can simply use the “toContain” matcher. This makes it much easier to read and understand the expectations, and can help reduce the amount of time spent debugging failed tests.

7. Use Jasmine Clock API to control time-dependent code

The Jasmine Clock API is a powerful tool that allows you to control the execution of time-dependent code. It works by overriding the JavaScript Date object, which is used for timing operations in many libraries and frameworks. By using the Jasmine Clock API, you can easily manipulate the passage of time within your tests, allowing you to test asynchronous behavior without having to wait for real-time delays.

Using the Jasmine Clock API is simple. To start, you need to call jasmine.clock().install() before any of your tests run. This will install the clock into the global scope, so it’s available to all of your tests. Then, when you want to manipulate the passage of time, you can use the tick() method. The tick() method takes an argument specifying how much time should pass (in milliseconds). For example, if you wanted to advance the clock by one second, you would call jasmine.clock().tick(1000). You can also use the mockDate() method to set the clock to a specific date and time.

8. Use custom matchers to make tests more readable

Custom matchers allow developers to create their own assertions that can be used in tests. This is beneficial because it allows for more expressive and readable test code, as the custom matcher names are often much easier to understand than the underlying Jasmine assertion functions. For example, instead of using expect(x).toBeGreaterThan(y), a developer could use a custom matcher called toBeLargerThan which would make the intent of the test clearer.

Creating custom matchers is also relatively straightforward. Developers simply need to define a new function within the beforeEach() block of their spec file, and then call this function from within an expectation. The custom matcher should take two parameters – the actual value being tested and the expected value – and return true or false depending on whether the comparison passes or fails. It’s important to note that custom matchers must always return either true or false; they cannot throw errors or return any other values.

Using custom matchers also makes debugging easier, since the name of the custom matcher will appear in the error message if the test fails. This helps developers quickly identify what went wrong with the test without having to dig into the code. Additionally, custom matchers can be reused across multiple specs, making them even more efficient.

9. Create helper functions or modules to keep test code DRY

DRY stands for “Don’t Repeat Yourself,” and it’s a programming principle that encourages developers to write code that is concise, efficient, and easy to maintain. When writing tests with Jasmine, DRY principles can be applied by creating helper functions or modules that are used in multiple test suites. This helps keep the codebase organized and reduces the amount of duplicate code.

Creating helper functions or modules also makes it easier to debug tests because all related logic is contained within one function or module. If there is an issue with the test, you only need to look at the helper function or module instead of searching through multiple test suites. Additionally, if changes need to be made to the test logic, they can be done quickly and easily since all the relevant code is located in one place.

When creating helper functions or modules, it’s important to make sure they are well-documented so other developers can understand what the code does. It’s also helpful to include comments throughout the code to explain any complex logic. Finally, it’s best practice to create unit tests for each helper function or module to ensure that it works as expected.

10. Use async/await syntax with Promises to handle asynchronous operations

When using Jasmine, it is important to use async/await syntax with Promises because it allows for more readable and maintainable code. Async/await syntax makes asynchronous operations easier to read and understand by allowing the code to be written in a synchronous-like manner. This means that instead of having to write nested callbacks or chaining multiple promises together, you can simply await the result of an asynchronous operation before continuing on with the rest of your code.

Using async/await syntax also helps make debugging easier since errors are thrown at the same line as the awaited promise, rather than being buried deep within a callback function. Additionally, when using async/await syntax, you don’t have to worry about forgetting to return a Promise from a test case, which could lead to unexpected results.

To use async/await syntax with Promises in Jasmine, you need to wrap any asynchronous code inside an async function. Then, you can use the await keyword to wait for the result of a Promise before continuing on with the rest of the code. For example, if you wanted to wait for a Promise to resolve before logging out its value, you would do something like this:

async function myFunction() {
const result = await somePromise();
console.log(result);
}

It’s important to note that when using async/await syntax, you should always catch any potential errors that may occur. If an error occurs while awaiting a Promise, it will be thrown and must be caught in order to prevent the test from crashing. To catch errors, you can use a try/catch block like so:

async function myFunction() {
try {
const result = await somePromise();
console.log(result);
} catch (err) {
// Handle error here
}
}