我试图通过模拟用于从外部API获取数据的函数来测试react组件，该函数是从useEffect钩子中调用的。但是我得到以下错误
Cannot read properties of undefined (reading 'then') TypeError: Cannot read properties of undefined (reading 'then')
我已经尝试过用useEffect将函数定义从中分离出来，以提高可测试性，但也可以使用一些指针。
根据建议，我尝试将数据获取和组件分离，以提高可测试性。
数据获取和测试组件的示例如下所示：
数据提取的定义为：

// api.ts

import {EmployeeModel} from "../models/EmployeeModel";

export async function getAllEmployees(): Promise<EmployeeModel[]> {
    const baseUrl: string = "http://localhost:8080/employees";
    const response: Response = await fetch(baseUrl);
    const responseJson = await response.json();
    const employees: EmployeeModel[] = [];

    for (let key in responseJson) {

        const emp: EmployeeModel = new EmployeeModel(
            responseJson[key].name,
            responseJson[key].gender,
            responseJson[key].address,
            responseJson[key].postcode,
            responseJson[key].department,
            responseJson[key].salary,
            responseJson[key].email,
            responseJson[key].employeeNumber
        );

        employees.push(emp);
    }
    return employees;
}

测试的组件：

// React component

import React, {useEffect, useState} from "react";
import {JSX} from "react";
import {EmployeeTable} from "./EmployeeTable";
import {EmployeeModel} from "../models/EmployeeModel";
import {getAllEmployees} from "../services/EmployeeApiService";
import {Simulate} from "react-dom/test-utils";
import {EmployeeDataTransferModel} from "../models/EmployeeDataTransferModel";

export const EmployeeTableWrapper: React.FC<{}> = (props): JSX.Element => {

    const [employees, setEmployees] = useState<EmployeeModel[]>([]);

    useEffect((): void => {

        getAllEmployees()
            .then((response: EmployeeModel[]): void => {
                setEmployees(response)
            })
            .catch((error: any) => {
        });
       // setIsLoading(false);

    }, [getAllEmployees])

    return (
        <EmployeeTable employees={employees}/>
    )
}

和所创建的测试：

Finally the test that has been written so far (I have removed the asserts until the I can get the test passing):

`import React from 'react';
import {render, screen} from '@testing-library/react';
import {EmployeeTableWrapper} from "../../components/EmployeeTableWrapper";
import {getAllEmployees} from "../../services/EmployeeApiService";
import {EmployeeModel} from "../../models/EmployeeModel";

const mockEmployees: EmployeeModel[] = [
    new EmployeeModel(
        "Test_User",
        "M",
        "3 Fake Street",
        "M1",
        5,
        "Tech",
        23000.0,
        "test2test.com")
]

jest.mock("../../services/EmployeeApiService", () => ({
    getAllEmployees: jest.fn(() => Promise.resolve(mockEmployees))
}));

describe("EmployeeTableWrapper", () => {
    it('should ', async function () {

       await act(async() => {
            render(<EmployeeTableWrapper />)

            await getAllEmployees();
        })

    });
});`

任何建议将不胜感激。