Jest looping through dynamic test cases

user_3096159 0
Viewed 81934

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);
                });
            }
        });
    
    });
jestjs node.js unit-testing javascript
6 Answers

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.

user_9901590

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

user_30961590

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);
  });
})
user_21710400

An alternative solution:

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

describe("Test cases for math module", () => {
  cases.forEach((el, i) => {
    let value1 = el.q[0]
    let value2 = el.q[1]
    let value3 = el.r

    test(`the sum of ${value1} and ${value2} equals ${value3}`, () => {
      expect(value1 + value2).toBe(value3)
    })
  })
})

Test results

When all tests pass:

enter image description here

In case one or more tests fail, it will show like so:

enter image description here

I did all the tests in CodeSandbox, if you want to play with the code click here

user_148959850

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);
    }
  }
});
user_71065650
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