pg-promise spy on query functions

Is it possible to spy on pg-promise's query functions (query(), one(), none(), ...)?

The following example fails with the error message TypeError: Cannot assign to read only property 'none' of object '[object Object]':

const db = pgPromise()({ /* ... */ });

jest.spyOn(db, 'none');

Using jest.spyOn(db, 'none', 'get'); does not work either.