Error when testing a component that invokes an apex method which return value is not mocked

[jodarove]

Description

A test for a component that programmatically invokes an apex method (without mocked return value) fails with the error TypeError: Cannot read property 'then' of undefined.

Steps to Reproduce

  <h1>Todos</h1>
  <ul>
      <template for:each={todos} for:item="todo">
         <li key={todo.id}>{todo.name}</li>
      </template>
  </ul>

import { LightningElement } from 'lwc';
import getTodos from '@salesforce/apex/Foo.getTodos';

export default class TodoList extends LightningElement {
    todos = [];

    connectedCallback() {
        getTodos()
                .then((result) => {
                    this.todos = result;
                });
    }
}

Test:

import { createElement } from 'lwc';
import TodoList from 'c/todo-list';

describe('c-todos', () => {
    it('should render h1', () => {
        const element = createElement('c-todo-list', {
            is: TodoList
        });
        document.body.appendChild(element);

        return Promise.resolve().then(() => {
            expect(element.shadowRoot.querySelector('h1')).not.toBeNull();
        });
    });
});

Expected Results

Test passes

Actual Results

TypeError: Cannot read property 'then' of undefined

Version

• @salesforce/sfdx-lwc-jest: 0.12.3

(in v0.11.0 it passes)

Possible Solution
In v0.11.0, apex methods were auto-mocked to a function returning a Promise.resolve(). With 0.12.3 (#208) they are auto-mocked to a jest.fn() without return value.