Utilize a jest mock object and pass it as a method parameter to achieve seamless testing

I am attempting to create a mock object (ColumnApi from ag-grid) using jest and then pass it as a parameter to a function that calls the "getAllColumns" method from ColumnApi. I am not concerned with how the "getAllColumns" method functions, but I want it to return a specific array of Columns (Column[]). How can I design this object/mock to achieve both:

  • passing it as a parameter to a function that requires the ColumnApi type
  • mocking the return value of a function within this object

Test:

describe("test", () => {
   
    // my unsuccessful attempts to create the mock/object:

    // let columnApi: ColumnApi {};

    // const spyInstance = jest.spyOn(columnApi, "getAllColumns");
    // const mock = jest.fn().mockImplementation(() => "abc");

    // jest.mock("@ag-grid-community/core/dist/cjs/columnController/columnApi", () => columnApi);

    // const columnApiSpy = jest.spyOn(ColumnApi, "getAllColumns");
    //
    // jest.mock("./main", () => ({
    //     columnApi: ,
    // }));
    // let columnApiMock: jest.Mock<ColumnApi>;

    const params = {
        columnApi: columnApi,
    }

    beforeEach(async () => {
        await repository.getRows(params);
    });
});

"getRows" function from repository:

getRows(columnApi: ColumnsApi) {
    
    columnApi.getAllColumns());

}

Answer №1

In my opinion, the key is to simulate the behavior of the spy. It would be advisable to do this within the beforeEach function (ensuring that jest can reset the spy between tests).

import api from '@ag-grid-community/core/dist/cjs/columnController/columnApi'

describe('unit test', () => {
  beforeEach(() => {
    jest.spyOn(api, 'getAllColumns').mockImplementation(() => "xyz")
    await repository.fetchData({ api });
  })
})

The specifics of how the api variable is defined or imported aren't important – what matters is replacing its functionality.

Answer №2

To solve the issue at hand, I simply had to generate a new object with the method "getAllFunctions" clearly defined. Here is how I accomplished this:

let entries: Entry[] = {};
let entryApi: {
getEntriesList: entries,
}

Subsequently, I was able to transfer the object entryApi to the parameters object and forward it to the database.fetchEntries function. Instead of resorting to mocking or spying, crafting a custom object with appropriate types proved to be the optimal approach.

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