Inifnite render error when setting value via useState inside a useEffect only when testing

Question

I have the following simple component where I am just looking to set a value at the start.

Thus trying to set the value inside useEffect.

I have simplified the component to be minimal here.
As long as I try to set the value via useState, it throws following error.

Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.

It it not the externalFunction. Issue is with using the useState setter itself since even setting it to true throws same error.

Why is this an issue?

If I try to do a counter inside here, I only enter useEffect once when I comment out setValid.
But if I call setValid, I enter useEffect about 25 times before erroring.

How could I rectify this issue. I need to set this value via useState for use further down in the component. Please advice.

Code:

export const MyComponent = () => {
  const [valid, setValid] = React.useState(undefined);
  React.useEffect(() => {
    setValid(externalFunction());
    // setValid(true); // same error
  }, []);

  return <MyComponent />;
};

This works fine when I run it. The error comes from running following test.

import { shallow } from 'enzyme';
const render = (props) => shallow(
    <MyComponent
        {...props}
    />
);

it('should render', () => {
    const renderedModule = render();
    expect(renderedModule).toMatchSnapshot();
});

Answer 1

The example as given does not cause a recursive render. See this sandbox.

If you need to set the initial value of a state to a function return value, though, setState can take a function to call for its initial value:

export const MyComponent = () => {
  const [valid, setValid] = useState(externalFunction);
  // Or more verbosely:
  // const [valid, setValid] = useState(() => externalFunction());

  return <div>test</div>;
};