How to define a type for mocked function in node test?

[varunkamra]

Let’s say I have a class called Base

abstract class Base {
  public async call() {
     // some logic
  }
}

In unit test I have to mock call function and need to verify that the mock was called. To achieve this I am currently using the following logic:

mock.method(Base.prototype, “call”).mock.mockImplementation(async() => {
   // something here
  });

assert.equal(Base.prototype.call.mock.callCount(), 1);

Typescript shows error in VS code where .mock in the assert is underlined in red which says property mock does not exist on function call. Do you know how to add a custom type to make this red squiggly underline fixed?

Node version: 20 LTS

[varunkamra]

Found a solution on stackoverflow. I had to define a custom type like this:

type GenericFunction {
  (): any,
  mock: any
}

then use the type to typecast like following:

assert.equal((<GenericFunction>Base.prototype.call).mock.callCount(), 1);