It's not possible to mock classes with static methods using jest and ts-jest - node.js

Question

I have two classes that simulate a simple sum operation.
import SumProcessor from "./SumProcessor";
class Calculator {
constructor(private _processor: SumProcessor) { }
sum(a: number, b: number): number {
return this._processor.sum(a, b)
}
}
export default Calculator
And the operation processor.
class SumProcessor {
sum(a: number, b: number): number {
return a + b
}
static log() {
console.log('houston...')
}
}
export default SumProcessor
I'm tryng to mock the class SumProcessor to write the following unit test using jest+ts-jest.
import Calculator from "./Calculator"
import SumProcessor from "./SumProcessor"
import { mocked } from "ts-jest/utils"
jest.mock('./SumProcessor')
describe('Calculator', () => {
it('test sum', () => {
const SomadorMock = <jest.Mock>(SumProcessor)
SomadorMock.mockImplementation(() => {
return {
sum: () => 2
}
})
const somador = new SomadorMock()
const calc = new Calculator(somador)
expect(calc.sum(1, 1)).toBe(2)
})
})
When the static method is present in class SumProcessor, the mock code const SomadorMock = (SumProcessor) indicates the following compilation error:
TS2345: Argument of type '() => jest.Mock<any, any>' is not assignable to parameter of type '(values?: object, option
s?: BuildOptions) => SumOperator'.
Type 'Mock<any, any>' is missing the following properties from type 'SumOperator...
If the static method is removed from SumProcessor class, everything work's fine.
Can anybody help?

Answer 1

since you have already mocked the SumProcessor class with jest.mock('./SumProcessor'); you can just add a spy to the method you would like to mock, for an example:
jest.spyOn(SumProcessor.prototype, 'sum').mockImplementation(() => 2);
this way your test class would look something like this:
import Calculator from "./Calculator"
import SumProcessor from "./SumProcessor"
jest.mock('./SumProcessor')
describe('Calculator', () => {
it('test sum', () => {
jest.spyOn(SumProcessor.prototype, 'sum').mockImplementation(() => 2);
const somador = new SumProcessor();
const calc = new Calculator(somador)
expect(calc.sum(1, 1)).toBe(2)
})
})
much simpler, right?