Jest test init conditions - jestjs

Question

Lets say I have a file file1.js which contains:
const a = true;
let b;
if (a) {
b = c;
}
if (!a) {
b = d;
}
Now when I run test case on this file my first condition gets covered. Is there any way that I can cover second condition by setting a to false or should I change my code in a way that I can call a method with different values to test for each case kind of like:
const a = true;
getBVal(a) {
return a ? c : d;
}
let b = getBVal(a);
Update:
Below is my code for requestAnimationFrame with fallbacks for older browsers:
let lastTime = 0;
const vendors = ["ms", "moz", "webkit", "o"];
let rAF = window.requestAnimationFrame;
if (!rAF) {
rAF = vendors.find(prefix => window[`${prefix}RequestAnimationFrame`]);
}
if (!rAF) {
rAF = cB => {
const currTime = new Date().getTime();
const timeToCall = Math.max(0, 16 - (currTime - lastTime));
const id = setTimeout(() => {
cB(currTime + timeToCall);
}, timeToCall);
lastTime = currTime + timeToCall;
return id;
};
}
function requestAnimationFrame(callback) {
return rAF(callback);
}
export default requestAnimationFrame;
I am using jsdom in setup for window object. Now if I have to test case for window.requestAnimationFrame = null its not possible in the way I have written my code
Now after changing it to:
import { requestAnimationFrameVendor } from "../constants";
let lastTime = 0;
const customFn = cB => {
const currTime = new Date().getTime();
const timeToCall = Math.max(0, 16 - (currTime - lastTime));
const id = setTimeout(() => {
cB(currTime + timeToCall);
}, timeToCall);
lastTime = currTime + timeToCall;
return id;
};
function requestAnimationFrame(callback) {
const rAF = window.requestAnimationFrame;
return rAF && rAF(callback) || requestAnimationFrameVendor && requestAnimationFrameVendor(callback) || customFn(callback);
}
export default requestAnimationFrame;
And then if I write test like:
import * as constants from "../../constants";
describe("animationFrame", () => {
let requestAnimationFrame;
let cancelAnimationFrame;
beforeAll(() => {
requestAnimationFrame = global.window.requestAnimationFrame;
cancelAnimationFrame = global.window.cancelAnimationFrame;
});
test("requestAnimationFrame", done => {
global.window.requestAnimationFrame = null;
global.window.cancelAnimationFrame = null;
const requestId1 = Utils.requestAnimationFrame(jest.fn());
constants.requestAnimationFrameVendor = jest.fn(() => {
return requestAnimationFrame;
});
const requestId2 = Utils.requestAnimationFrame(jest.fn());
setTimeout(() => {
Utils.cancelAnimationFrame(requestId1);
Utils.cancelAnimationFrame(requestId2);
done();
}, 300);
});
afterEach(() => {
global.window.webkitRequestAnimationFrame = null;
global.window.webkitCancelAnimationFrame = null;
});
});
Then it covers all the conditions.

Answer 1

I would go the second rout (getBVal()) because it makes your interface more testable.
In general, removing global state (like your const a or let b) will make your code and interfaces more testable. If you cannot remove the global state completely, you can introduce abstractions so that your test does not need to know about the global state (like your suggested getBVal()).
Maybe you can go even further and remove the global b: Instead always call getBVal() instead? The performance impact will be negligible in most cases, and your code becomes even more testable and less coupled...