Jest SpyOn choose the correct overload

user_200759 0
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I do have a class that has 2 overloaded methods.

  public static create<M extends Model>(
    this: ModelStatic<M>,
    values?: M['_creationAttributes'],
    options?: CreateOptions<M['_attributes']>
  ): Promise<M>;
  public static create<M extends Model>(
    this: ModelStatic<M>,
    values: M['_creationAttributes'],
    options: CreateOptions<M['_attributes']> & { returning: false }
  ): Promise<void>;

in my unit test, I'm trying to use jest.spyOn to mock the first method however jest sees only the one that returns Promise<void>.

const mockInsightCreate = jest.spyOn(Insight, "create");
mockInsightCreate.mockReturnValue(Promise.resolve()); // here I need to return an object of type - Insight

Is there a way to instruct spyOn to pickup the first method that returns Promise<M> ?

import {
    Model,
} from "sequelize-typescript";

... 

export default class Insight extends Model<Insight> {
sequelize.js jestjs typescript reactjs
1 Answers

I know this question is old, but bellow is my answer for anyone facing the same issue who might stumble across it.

There is currently no way of instructing which overload signature spyOn should use. One solution would be to cast the value to whatever spyOn expects.

mySpy.mockReturnValue(Promise.resolve(myObj) as unknown as void);
mySpy.mockResolveValue(myObj as unknown as void);

However, I personally prefer avoiding coercing the typing system if possible. Another workaround that does not require any typing judo is to mock the entire method implementation.

mySpy.mockImplementation(() => Promise.resolve(myObj));
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