saveStudentsMeanGrade.test.js

import { saveStudentsMeanGrade } from '../saveStudentsMeanGrade';
import { saveStudents } from '../../infra/database/saveStudents';

jest.mock('../../infra/database/saveStudents');

describe('saveStudentsMeanGrade', () => {
  it('correctly update students mean grade', async () => {
    // arrange
    let savedStudentsMeans;
    saveStudents.mockImplementation(studentsMeans => {
      savedStudentsMeans = studentMeans;
      return Promise.resolve();
    });
    const students = [
      {
        name: 'Paul',
        grades: [10, 15.5, 8, 12],
      },
      {
        name: 'Sophie',
        grades: [18, 16, 9.5],
      },
      {
        name: 'Julie',
        grades: [5.75, 10, 11.5, 8, 14],
      },
    ];
    
    // act
    await saveStudentsMeanGrade(students);
    
    // assert
    expect(savedStudentsMeans).toEqual([
      {
        name: 'Paul',
        mean: 11.375,
      },
      {
        name: 'Sophie',
        mean: 14.5,
      },
      {
        name: 'Julie',
        mean: 9.85,
      },
    ]);
  })
})