ts-mockito: When mocking a function named `execute`, I get "execute is not a function"

Question

I am testing a typescript project with ts-mockito and jest. Getting errors like this on a function called execute:

Error: 'MyAbstractClass.execute' is not a function

// main.ts
abstract class MyAbstractClass {
  abstract execute(arg): Promise<any>;
}

class MyImplementedClass extends MyAbstractClass {
  execute(arg): Promise<any> {
    // ... do some stuff
    return foo;
  }
}

// main.test.ts
describe(... {
  let mockMyAbstractClass: MyAbstractClass;
  let myAbstractClassInstance: MyAbstractClass;

  beforeEach(() => {
      mockMyAbstractClass = mock(MyAbstractClass);
      myAbstractClassInstance = instance(mockMyAbstractClass);
  });
 
  it('works', async () => {
    // ...
    when(mockMyAbstractClass.execute(input)).thenResolve(output); // error is on this line
  });
});

I've tried setting mocks on the prototype and using jest.fn() to help with mocking to no avail.

Answer 1

It seems like you need to define and instantiate your subclass for the mock to work:

// Before
  let mockMyAbstractClass: MyAbstractClass;
  let myAbstractClassInstance: MyAbstractClass;

  beforeEach(() => {
      mockMyAbstractClass = mock(MyAbstractClass);
      myAbstractClassInstance = instance(mockMyAbstractClass);
  });

// After
  let mockMyAbstractClass: MyClass;
  let myAbstractClassInstance: MyClass;

  beforeEach(() => {
      mockMyAbstractClass = mock(MyClass);
      myAbstractClassInstance = instance(mockMyAbstractClass);
  });