How Can I Write A Test Which Expects An Error To Be Thrown In Jasmine

When writing tests in Jasmine, ensuring that your code behaves as expected in all scenarios is crucial. One common scenario is verifying that an error is thrown when it should be in your application. In this guide, we will walk you through how to write a test that expects an error to be thrown in Jasmine, the popular JavaScript testing framework.

To set up a test that expects an error to be thrown in Jasmine, you can use the `toThrow()` matcher provided by Jasmine. This matcher allows you to check whether a function throws an exception when it is called. Let's dive into how you can implement this in your tests.

First, you need to define the test block using the `it()` function provided by Jasmine. Inside the `it()` block, write an anonymous function that contains the code you want to test for an error. This code snippet should invoke the function that you expect to throw an error.

Next, you will use the `expect()` function to set up the assertion. Within the `expect()` function, you will call the function that is expected to throw an error. After calling the function, you can use the `toThrow()` matcher to specify that you expect the function to throw an error.

Here's an example to illustrate how you can write a test that expects an error to be thrown in Jasmine:

describe('Error handling', function() {
  it('should throw an error when a certain condition is met', function() {
    function throwError() {
      throw new Error('Something went wrong');
    }

    expect(throwError).toThrow();
  });
});

In this example, the test expects the `throwError` function to throw an error. If the function does not throw an error when invoked, the test will fail, indicating that the expected error was not thrown.

It's important to note that when working with asynchronous code that throws errors, you need to handle promises appropriately in Jasmine. You can utilize `async/await` or Jasmine's `done` function to test asynchronous functions that are expected to throw errors.

Remember to provide descriptive error messages when throwing errors in your functions. This will help you identify the source of the error more easily when running your tests.

In conclusion, writing tests that expect errors to be thrown in Jasmine is essential for ensuring the robustness of your code. By using Jasmine's `toThrow()` matcher and structuring your tests effectively, you can verify that your code handles errors as expected. Happy testing!