Jest looping through dynamic test cases

If anyone wondering how this can work for a single input function here is an example

const testData = [
      ['input1', 'output1'],
      ['input2', 'output2'],
      ['input3', 'output3'],
]

test.each(testData)('myFunc work correctly for %s',(input, output) =>{
        expect(yourFunc(input)).toBe(output)
})

https://jestjs.io/docs/en/api#testeachtablename-fn-timeout

You can use classic JS, it is more readable and with less code:

[
  { input: [2, 3], output: 5 },
  { input: [1, 2], output: 3 },
].forEach(({ input, output }) => {
  it(`works correctly for ${input}`, () => {
    // ...

    expect(...).toBe(output);
  });
})

If one passes, they all will. So you only need one for a positive test. Ideally, you want 1 positive where the 2 numbers equal the sum, and a failure where you pass a string or something and throw an error.

TL/DR; You don't need 4 tests that all do the same thing. Also, you need to pull the looped test cases out of the parent test for the loop to work.

This will work just fine:

import jest from 'jest';
import { sumModule } from './';

const tests = [
  {x: 1, y: 2, r: 3}, 
  {x: 3, y: 4, r: 7}
];

describe('Adding method', () => { 
    for(let i = 0; i < tests.length; i++){
      it('should add its params', () => {
        const actual = sumModule(tests[i].x, tests[i].y);
        expect(actual).toBe(tests[i].r);
      });
    }
});

There's an in-built way to do this: test.each(table)(name, fn, timeout)

e.g.

test.each([[1, 1, 2], [1, 2, 3], [2, 1, 3]])(
  '.add(%i, %i)',
  (a, b, expected) => {
    expect(a + b).toBe(expected);
  },
);

where each inner array in the 2D array is passed as args to the test function.