jest tests for Axios.all and Axios.spread - vue.js

Question

I am struggling to write JEST test cases for below method
getStudentList (studentList:}[]) {
if (studentList.length < 1) {
Promise.resolve()
}
let promises = []
for (const student of StudentList) {
if (!student.name) {
Promise.resolve()
}
var url = `${API_URL}/${student.name}/`
promises.push(Axios.get(url}))
}
return Axios.all(promises)
.then(Axios.spread((...args) => {
// customise the response here
return args
.map(response => response.data)
.map(data => {
//do something with data
return data
})
}))
It uses axios.all and axios.spread to get the data back..i have written simple test cases for Axios.get..but how to write test case for this? This method is in a vue project in a service class

Answer 1

This is a short example of how you can write your expectations (with 100% coverage) for the code above:
import myService from './myService';
import Axios from 'axios';
jest.mock('axios');
global.API_URL = 'http://example.com/mock_api';
describe('myService', () => {
describe('getStudentList', () => {
describe('without students in the list', () => {
it('should result undefined', () => {
const result = myService.getStudentList();
expect(result).resolves.toEqual( undefined );
});
});
describe('with students in the list', () => {
const mockStudentList = [{
name: 'student1',
}, {
someProp: 'some value',
}, {
name: 'student3',
}];
const results = [];
const mockAxiosSpreadResult = jest.fn();
beforeAll(() => {
Axios.get.mockClear();
Axios.all.mockResolvedValue(results);
Axios.spread.mockReturnValue(mockAxiosSpreadResult);
myService.getStudentList( mockStudentList );
});
it('should call Axios.get once for each student with name', () => {
expect(Axios.get).toHaveBeenCalledWith(`${API_URL}/student1/`);
expect(Axios.get).toHaveBeenCalledWith(`${API_URL}/student3/`);
});
it('should call Axios.spread with a callback', () => {
expect(Axios.spread).toHaveBeenCalledWith(expect.any(Function));
});
it('should call the result of Axios.spread with the resolved value of Axios.all', () => {
expect(mockAxiosSpreadResult).toHaveBeenCalledWith(results);
});
describe('Axios.spread callback', () => {
let callback;
beforeAll(() => {
callback = Axios.spread.mock.calls[0][0];
});
describe('called with parameters', () => {
let result;
beforeAll(() => {
result = callback({
data: 1
},{
data: 2
},{
data: 3
},{
data: 4
});
});
it('should do something with the data', () => {
expect(result).toEqual([1,2,3,4]);
});
});
});
});
});
});
working example