How to mock a class being imported from a npm module - react-native

Question

I am importing a class via const { PaymentRequest } = require("react-native-payments"); and I am trying to mock the functions it exposes when it is instantiated. For example:
const paymentRequest = new PaymentRequest(METHOD_DATA, DETAILS, OPTIONS);
paymentRequest.canMakePayments().then(res => {...})
I want to mock this and change the value coming back from the promise resolve so that I can test different scenarios from canMakePayments and other async functions the class exposes.

Answer 1

Here is the solution, you can use jest.mock method mock react-native-payments module manually.
index.ts:
const { PaymentRequest } = require('react-native-payments');
const METHOD_DATA = [
{
supportedMethods: ['apple-pay'],
data: {
merchantIdentifier: 'merchant.com.your-app.namespace',
supportedNetworks: ['visa', 'mastercard', 'amex'],
countryCode: 'US',
currencyCode: 'USD'
}
}
];
const DETAILS = {
id: 'basic-example',
displayItems: [
{
label: 'Movie Ticket',
amount: { currency: 'USD', value: '15.00' }
}
],
total: {
label: 'Merchant Name',
amount: { currency: 'USD', value: '15.00' }
}
};
const OPTIONS = {
requestPayerName: true
};
function main() {
const paymentRequest = new PaymentRequest(METHOD_DATA, DETAILS, OPTIONS);
return paymentRequest.canMakePayment();
}
export { main, METHOD_DATA, DETAILS, OPTIONS };
main function is going to be tested.
index.spec.ts:
import { main, METHOD_DATA, DETAILS, OPTIONS } from './';
const { PaymentRequest } = require('react-native-payments');
jest.mock('react-native-payments', () => {
const PaymentRequestMocked = {
canMakePayment: jest.fn()
};
return {
PaymentRequest: jest.fn(() => PaymentRequestMocked)
};
});
const paymentRequest = new PaymentRequest(METHOD_DATA, DETAILS, OPTIONS);
describe('main', () => {
beforeEach(() => {
paymentRequest.canMakePayment.mockReset();
});
it.each`
value | name
${'mocked value 1'} | ${'t1'}
${'mocked value 2'} | ${'t2'}
`(`$name`, async ({ value }) => {
paymentRequest.canMakePayment.mockResolvedValueOnce(value);
const actualValue = await main();
expect(actualValue).toEqual(value);
expect(paymentRequest.canMakePayment).toBeCalledTimes(1);
});
});
Unit test result with 100% coverage:
PASS src/stackoverflow/57565053/index.spec.ts
main
✓ t1 (5ms)
✓ t2 (1ms)
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 100 | 100 | |
index.ts | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 2 passed, 2 total
Snapshots: 0 total
Time: 3.03s, estimated 6s
Here is the completed demo: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/57565053