How to use CodeceptJS to unit-test a JS function - unit-testing

Question

I've set up CodeceptJS for a project and use it to test various end-to-end scenarios.
Now I want to extend the tests-suite to also run unit-tests to verify functionality of custom JS functions.
For example: I have a global object App that has a version attribute. As a first test, I want to confirm that App.version is present and has a value.
My first attempt is a test.js file with the following code:
Feature('Unit Tests');
Scenario('Test App presence', ({ I }) => {
I.amOnPage('/');
I.executeScript(function() {return App.version})
.then(function(value) { I.say(value) } );
});
Problems with this code
The major issue: How can I assert that the App.version is present?
My script can display the value but does not fail if it's missing
My code is very complex for such a simple test.
I'm sure there's a cleaner/faster way to perform that test, right?

Answer 1

Here is a solution that works for me:
Read data from the browser:
I created a custom helper via npx codecept gh and named it BrowserAccess.
The helper function getBrowserData uses this.helpers['Puppeteer'].page.evaluate() to run and return custom code from the browser scope. Documentation for .evaluate()
Custom assertions:
Install the codeceptjs-assert package, e.g. npm i codeceptjs-assert
Add the AssertWrapper-helper to the codecept-config file. This enables checks like I.assert(a, b)
Full Code
codecept.conf.js
exports.config = {
helpers: {
AssertWrapper: {
require: "codeceptjs-assert"
},
BrowserAccess: {
require: './browseraccess_helper.js'
},
...
},
...
}
browseraccess_helper.js
const Helper = require('#codeceptjs/helper');
class BrowserAccess extends Helper {
async getBrowserData(symbolName) {
const currentPage = this.helpers['Puppeteer'].page;
let res;
try {
res = await currentPage.evaluate((evalVar) => {
let res;
try {
res = eval(evalVar);
} catch (e) {
}
return Promise.resolve(res);
}, symbolName);
} catch (err) {
res = null;
}
return res;
}
}
jsapp_test.js (the test is now async)
Feature('Unit Tests');
Scenario('Test App presence', async ({ I }) => {
I.amOnPage('/');
const version = await I.getBrowserData('App.version');
I.assertOk(version);
});