Parameterized Tests with Jest

In my other blog, we understood what is a parameterized test. Now as part of this article, we’ll try to understand how to do it using Jest. So, let’s write some code to understand how it’s possible.

Option 1:

First of all, we have to add jest-each package to our devDependencies . Once we have the dependency then we can start declaring a test method with parameters.

const isPalindrome = require("../utils").isPalindrome;
const each = require("jest-each").default;

describe("isPalindrome", () => {
  each([
    ["madam", true],
    ["car", false]
  ]).it("when the input is '%s'", (text, expected) => {
    expect(isPalindrome(text)).toBe(expected);
  });
});

Option 2:

If you use Jest ≥ 23.x, then you don’t have to install any additional package. Same behaviour can be achieved by in-built method.

describe("isPalindrome", () => {
  it.each([
    ["madam", true],
    ["car", false]
  ])("when the input is '%s'", (text, expected) => {
    expect(isPalindrome(text)).toBe(expected);
  });
});

And that’s it. Now we have a test to validate our isPalindrome function with two different arguments ( madam and car ).

Now let’s check the output which will be same for Option 1 and Option 2,

Note: Here we used es5 syntax to import the modules but we can use es6 syntax as well.

Conclusion

That’s all folks! I hope you’ve been able to understand that we can do the parameterized tests using Jest as well. Also as you observed jest-each package is easy and simple. To know more about jest-each package, check this out.

There are several npm packages to write parameterized tests. So, feel free to choose a library depends on your testing framework.