Jest looping through dynamic test cases

53
votes

How do I loop through dynamic test cases in Jest?

I have test cases like the following how do I dynamically create jest test case using it/test methods.

Here is what I have tried , However it just passes without excuting the test cases in the loop.

    const mymodule = require('mymodule');

    const testCases = [
        {q: [2, 3],r: 5},
        {q: [1, 2],r: 3},
        {q: [7, 0],r: 7},
        {q: [4, 4],r: 8}
    ];

    describe("Test my Math module", () => {
        test("test add method", () => {
            for (let i = 0; i < testCases.length; i++) {
                const { q,r } = testCases[i];
                it(`should  add ${q[0]},${q[1]} to ${expected}`, () => {
                    const actual = mymodule.add(q[0] + q[1]);
                    expect(actual).toBe(expected);
                });
            }
        });
    
    });
5
javascriptnode.jsunit-testingjestjs

5 Answers

86
votes

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.

26
votes

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);
      });
    }
});
8
votes

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

4
votes

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);
  });
})
0
votes

For loop works in jest, No need to use inbuilt function without any reason!

 test('adding positive numbers is not zero', () => {
  for (let a = 1; a < 10; a++) {
    for (let b = 1; b < 10; b++) {
      expect(a + b).not.toBe(0);
    }
  }
});