Testing functions with arguments in React with Jest Enzyme

Question

I have a function named toggleFilter() in a react component which looks like this:

toggleFilter = (filterType, filterName) => {
        const filterApplied = this.state.appliedFilterList[filterType].includes(filterName);

        if (filterApplied) {
            //Remove the applied filter
            this.setState(prevState => ({
                appliedFilterList: {
                    ...prevState.appliedFilterList,
                    [filterType]: prevState.appliedFilterList[filterType].filter(filter => filter !== filterName)
                }
            }));
        } else {
            //Add the filter
            this.setState(prevState => ({
                appliedFilterList: {
                    ...prevState.appliedFilterList,
                    [filterType]: [...prevState.appliedFilterList[filterType], filterName]
                }
            }));
        }
    };

This function is being passed to the child components as :

 <ChildComponent  toggleFilter={this.toggleFilter} />

So, i am trying to test this toggleFilter() function like this:

 it("checks for the function calls", () => {
    const toggleFilterMockFn = jest.fn();
    const component = shallow(
        <ProductList
            headerText="Hello World"
            productList={data}
            paginationSize="10"
            accessFilters={["a 1", "a 2"]}
            bandwidthFilters={["b 1", "b 2"]}
            termsFilters={["t 1", "t 2"]}
            appliedFilterList={appliedFilter}
            toggleFilter={toggleFilterMockFn}
        />
    );
    component.find(FilterDropdownContent).prop("toggleFilter")({ target: { value: "someValue" } });
});

But I get the error saying :

TypeError: Cannot read property 'includes' of undefined

What may be causing the issue? Can someone please help me with this.

EDIT 1: I tried the below test case:

expect(toggleFilterMockFn).toHaveBeenCalledWith(appliedFilter, "access");

But I get the below error :

expect(jest.fn()).toHaveBeenCalledWith(expected)

    Expected mock function to have been called with:
      [{"access": ["Access Type Of The Service"], "bandwidth": ["the allowed band width ", "the allowed band width"], "term": ["term associated with the service"]}, "access"]
    But it was not called.

Answer 1

You can't render a parent and test a child function like that. Instead, you should render <FilterDropdownContent /> directly, and then write a test that simulates an event (like click) and checks to see if the function was called.

Something like this for example:

import React from 'react';
import { shallow } from 'enzyme';

describe('<FilterDropdownContent />', () => {
  let wrapper, toggleFilter;
  beforeEach(() => {
    toggleFilter = jest.fn();
    wrapper = shallow(
      <FilterDropdownContent
        toggleFilter={toggleFilter}
      />
    );
  });

  describe('when clicking the .toggle-filter button', () => {
    it('calls `props.toggleFilter()` with the correct data', () => {
      wrapper.find('.toggle-filter').simulate('click');
      expect(toggleFilter).toHaveBeenCalledWith({ target: { value: 'someValue' } });
    });
  }):
});

In this example, clicking a link with the .toggle-filter class calls the function, but you should be able to adapt this to your specific implementation.