Module pattern variable returning undefined in test?

I have the following code below which returns certain data depending on NODE_ENV:

config.js

export const Config = (() => {
    let data;

    switch (process.env.NODE_ENV) {
        case 'development':
            data = '123';
            break;
        case 'production':
            data = '456'
            break;
        default:
            break;
    }

    return {
        data
    };
})();

This works well in my component when I set NODE_ENV. However in my test, I keep getting undefined as a result.

config.test.js

describe('Config', () => {
    test('returns correct data if NODE_ENV is development', () => {
        process.env = { ...process.env, NODE_ENV: 'development' };

        expect(Config.data).toBe('123'); // returns undefined, expected '123'
    });

    test('returns correct data if NODE_ENV is production', () => {
        process.env = { ...process.env, NODE_ENV: 'production' };

        expect(Config.data).toBe('456'); // returns undefined, expected '456'
    });
});

Again, Config.data works fine in my React component when I start it up, but I guess I need to somehow initialize this for it to work in my tests? Any advice would be appreciated!