In the previous article, we created a specialized expect
function that returns an object with assertions, but one of our assertion function's side effects is that as soon as one assertion fails, it throws an error, so other tests do not run. A testing framework exists to help the developer identify what is broken as soon as possible. We can ensure that we will provide more helpful error messages and by running all of our tests.
Let's create our own test
function to encapsulate our automated tests and abstract them. Also, we want to ensure that we will run all the tests with more helpful error messages.
Our test
function will accept a title
of the test and a callback
.
Because our test
function can throw an error, we will wrap it in a try-catch
statement. Inside the try
block, we will call our callback
, and if the callback throws an error, we will log it out.
To help a developer identify which functionality is broken, we will log the title
. For better visibility, we are adding ✅ and ❌ emojis.
const test = <T>(title: string, callback: () => T) => {
try {
callback()
console.log(`✅ ${title}`)
} catch (error) {
console.error(`❌ ${title}`)
console.error(error)
}
}
Now let's encapsulate our assertion to a function and pass it as a callback to our test
function.
test('add function', () => expect(add(8, 16)).toBe(24))
test('subtract function', () => expect(subtract(32, 16)).toBe(16))
Now, we can rerun our test file, but we need to look into the console instead of the tests
tab.
It is now clearly visible that the problem is inside our add
function, not in the subtract
.
❌ add function
Error: -8 is not equal to 24
✅ subtract function
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