Jest with Angular Test case failing with error from angular core TypeError: Cannot read...

I am writing test cases for an angular application using Jest. My angular.json file already has

"test": {
"builder": "@angular-builders/jest:run",
"options": {
"tsConfig": "tsconfig.spec.json",
"polyfills": [
"zone.js",
"zone.js/testing"
]
}
}


and my jest.config.json already has

module.exports = {
setupFilesAfterEnv: [
'./jest.setup.js'
],
collectCoverage: true,
verbose: true,
transform: {
'^.+\\.ts$': 'ts-jest',
},
moduleFileExtensions: ['ts', 'js', 'mjs', 'json', 'node'],
testPathIgnorePatterns: ['perf-.+\\.spec\\.ts'],
}


and my jest.setup.js already has

const { TextEncoder, TextDecoder } = require('util');
import { registerLocaleData } from '@angular/common';
import localeEn from '@angular/common/locales/en';

global.TextEncoder = TextEncoder;
global.TextDecoder = TextDecoder;
if (localeEn) {
registerLocaleData(localeEn);
} else {
throw new Error('Locale data is undefined.');
}


The code for my test case is really simple:

import { TestBed } from '@angular/core/testing'
import { ConfigurationService } from './configuration.service'

describe('ConfigurationService', () => {
let service: ConfigurationService

beforeEach(() => {
TestBed.configureTestingModule({})
service = TestBed.inject(ConfigurationService)
})

it('should be created', () => {
expect(service).toBeTruthy()
})
})



While running a test case using ng test, I get the following error.

at registerLocaleData (../../node_modules/@angular/core/fesm2022/core.mjs:22522:25)
at registerLocaleData (../../node_modules/@angular/common/fesm2022/common.mjs:2562:12)
at Object.<anonymous> (../../node_modules/@weald/src/app/app.module.ts:45:1)
at Object.<anonymous> (../../node_modules/@weald/src/app/app-shared.module.ts:3:27)
at Object.<anonymous> (../../node_modules/@weald/src/public_api.ts:3:15)
at Object.<anonymous> (../../node_modules/@weald/src/weald-ui-core.ts:5:15)
at Object.require (src/lib/configuration/configuration.service.ts:3:1)
at Object.<anonymous> (src/lib/configuration/configuration.service.spec.ts:2:1)


If I go to (../../node_modules/@angular/core/fesm2022/core.mjs:22522:25) and add a console.log statement, I see LocaleId is: en typeof is: string

So, if the typeof is string, I am unable to troubleshoot more why .toLowerCase is causing an issue here.

Thanks

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