Jest not passing test when throw error - ecmascript-6

Question

I'm testing my code with Jest and mocking http call with nock JSON response:
it('should throw error when record does not exists', async() => {
const noExistsJSONFile = path.join(__dirname, "../../../data/api/project/non-existing.json");
nock(__ROOT_API__)
.defaultReplyHeaders({ 'access-control-allow-origin': '*' })
.get('/projects/2500')
.replyWithFile(404, noExistsJSONFile);
const response = await getProject('/projects/2500');
expect(response).toThrowError(`${notExisting.errorMessage} (Code: ${notExisting.errorCode})`);
});
});
There is an async function which should fail if the status code is > 300 and create new Error:
export async function get(pathname) {
const params = {
headers: {
'Content-Type': 'application/json',
}
};
let response = await fetch(`${__ROOT_API__}${pathname}`, params);
if (!validateStatusCode(response)) {
var error = new Error(response.statusText)
error.response = response
throw error
}
return response.json();
}
At moment when I'm running test JEST is throwing:
11 | let response = await fetch(`${__ROOT_API__}${pathname}`, params);
12 | if (!validateStatusCode(response)) {
> 13 | var error = new Error(response.statusText)
14 | error.response = response
15 | throw error
16 | }
at _callee$ (src/services/project/project.js:13:19)
at tryCatch (node_modules/regenerator-runtime/runtime.js:62:40)
at Generator.invoke [as _invoke] (node_modules/regenerator-runtime/runtime.js:296:22)
at Generator.prototype.(anonymous function) [as next] (node_modules/regenerator-runtime/runtime.js:114:21)
at step (node_modules/babel-runtime/helpers/asyncToGenerator.js:17:30)
at node_modules/babel-runtime/helpers/asyncToGenerator.js:28:13
When I looking on chrome network traffic I response which I need. What is the reason behind JEST error

Answer 1

It's because you're starting the fetch, thus, throwing the error before the toThrowError matcher. Furthermore, this is an async call, which makes it a bit more complex to test, for this reason, instead of using the toThrow matcher which is used for sync functions calls, you can use a try/catch block with the await syntax, as explained in the documentation:
expect.assertions(1);
try {
await getProject('/projects/2500');
} catch (e) {
expect(e).toMatch(`${notExisting.errorMessage} (Code: ${notExisting.errorCode})`);
}
expect.assertions(1) tells jest to expect one assertion inside the test.

Answer 2

I done small changes to code - not working 100% as expected but close.
Change a little bit response function :
export async function get(pathname) {
const params = {
headers: {
'Content-Type': 'application/json',
}
};
let response = await fetch(`${__ROOT_API__}${pathname}`, params);
if (!validateStatusCode(response)) {
const res = await response.json();
throw new Error(res.errorMessage);
}
return response.json();
}
And test looks like this:
it('should throw error when record does not exists', async () => {
const noExistsJSONFile = path.join(__dirname, "../../../data/api/project/non-existing.json");
nock(__ROOT_API__)
.defaultReplyHeaders({ 'access-control-allow-origin': '*' })
.get('/projects/2500')
.replyWithFile(404, noExistsJSONFile);
try {
await getProject('/projects/2500');
} catch (error) {
expect(error).toEqual(new Error('error message'));
}
});