玩笑测试-TypeError：由于类属性未定义，无法读取未定义的属性“ getVariablesLength”

Question

我有一个包装aggrid的组件。周围的组件导入了我的DataHolder类，该类具有一个名为getVariablesLength()的功能。但是，每当我进行测试时，都会出现错误消息TypeError: Cannot read property 'getVariablesLength' of undefined。

这是特定于对ag-grid的反应。我正在使用酶和玩笑进行测试。我已经研究了各种模拟导入的es6模块的方法，但是目前我不确定我是否正确理解了该过程。

//AGVariableGrid.ui.test.js

import AGVariableGrid from 'components/AGVariableGrid.jsx';
import Adapter from 'enzyme-adapter-react-16';
import { AgGridReact } from 'ag-grid-react';
import AgDataHolder from 'components/AgDataHolder.js';

//...

jest.mock(AgDataHolder);

beforeEach((done) => {
   console.log(mockDataHandler);
   component = mount(<AGVariableGrid/>);

   // get agGridReact instance in AGVariableGrid
   agGridReact = component.find(AgGridReact).instance();

   // ensure grid api has been set and other aggrid specific logic
});


test('all rows selected', () => {
    // no rows are selected initially

    expect(agGridReact.api.getSelectedRows().length).toEqual(0);

    // simulate a user clicking on the select all button
    component.find('#selectAll').simulate('click', {
        // no actual event data is needed for this particular event/use case
    });

    expect(agGridReact.api.getSelectedRows().length).toEqual(3);
});

在AGVariableGrid内

// ...
import AgDataHolder from 'components/AgDataHolder.js';
// ...

// in componentDidMount

this.dataHolder = new DataHolder();
const potato = this.dataHolder.getVariablesLength() // error on dataHolder being undefined

// ...

我真的很想知道为什么未定义它，或者如何正确模拟导入的类的属性。