How to test console.log output using Jest or other Javascript Testing Framework?

Question

I have a function that runs asynchronously, console logging the numbers 1 through 5 in order after a random setTimeout. I want to write a test for this function using Jest. How do I write one that tests that the console.log is 1, 2, 3, 4, 5 ?

Answer 1

Yes you can using jest.fn.

Here is an example:

File hello.js

console.log("Hello World");

File hello.test.js

let outputData = "";
storeLog = inputs => (outputData += inputs);
test("console log Hello World", () => {
  console["log"] = jest.fn(storeLog);
  require("./hello.js");
  expect(outputData).toBe("Hello World");
});