earlTesting errors
Often you want to assert that a given operation results in an error being thrown. That's what toThrow validator is useful in earl:
typescript
import { expect } from 'earljs'
function somethingThatCanThrow() {
throw new Error('Unexpected error!')
}
expect(() => somethingThatCanThrow()).toThrow('Unexpected error!')
When using toThrow we require you to pass parameterless function () => ... that will be executed and error will be caught. It's one of the limitation of JavaScript but don't worry! As long as you use TypeScript you will get a compile time error if you forget to do so.
Matching only part of an error message
You can combine toThrow with string matcher to for example to check if error message matches another string:
typescript
expect(() => somethingThatCanThrow()).toThrow(expect.stringMatching('Unexpected')
Expecting any error
typescript
expect(() => somethingThatCanThrow()).toThrow()
Expect a custom error
typescript
import { expect } from 'earljs'
class HttpError extends Error {
constructor(private readonly code: number) {
super(`Http error with code: ${code}`)
}
}
function somethingThatCanThrow() {
throw new HttpError(500)
}
expect(() => somethingThatCanThrow()).toThrow(
HttpError,
'Http error with code: 500',
)