How to test the return value of event handlers invoke via enzyme simulate?

Question

I want to test the return value of event handlers invoked via simulate

Given the react component:

// Example code
function SomeParentComponent() 
{
 const someExpression = ....;
 return <SomeComponent someEvent={() => someExpression ? true : false} />
}

and some test code:

// Test code
const wrapper = enzyme.shallow(<SomeParentComponent/>);
wrapper.find(SomeComponent).simulate('someEvent');
// TODO: verify the return value of someEvent handler.

The return value of simulate can't be used because Simulate returns a shallowWrapper (ie. wrapper.find(SomeComponent)), instead of the return value of the event handler.

I should add that in this case, the event handler doesn't modify state, so I can't test what it did, it's a call back function.

(And I was hoping to be able to do something better than wrapper.find(SomeComponent).instance().props().someEvent())

Answer 1

.invoke(invokePropName)(...args) => Any API can to this.

Invokes a function prop.

E.g.

index.tsx:

import React from "react";
import { useEffect } from "react";

export const SomeComponent = ({ someEvent }) => {
  useEffect(() => {
    someEvent()
  }, [])

  return <div>some component</div>
}

export function SomeParentComponent() {
  const someExpression = 1;
  return <SomeComponent someEvent={() => someExpression ? true : false} />
}

index.test.tsx:

import { shallow } from "enzyme"
import React from "react"
import { SomeParentComponent, SomeComponent } from "."

describe('76204394', () => {
  test('should pass', () => {
    const wrapper = shallow(<SomeParentComponent />);
    const actual = wrapper.find(SomeComponent).invoke('someEvent')()
    expect(actual).toBeTrue();
  })
})

Test result:

 PASS  stackoverflow/76204394/index.test.tsx (24.648 s)
  76204394
    ✓ should pass (33 ms)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |   72.73 |       50 |      50 |   66.67 |                   
 index.tsx |   72.73 |       50 |      50 |   66.67 | 5-9               
-----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        26.823 s

package version:

"enzyme": "^3.11.0",
"enzyme-adapter-react-16": "^1.15.5",
"react": "^16.14.0",