Should I test all component props? - reactjs

Question

For example, I have component like this:
const Button = ({borderColor, children}) => {
return (
<button style={{borderColor: borderColor ? `border: 1px solid ${borderColor}` : null}}>
{children}
</button>
)
}
Main goals of this component are:
pass children prop further
handle custom border color
With children - it's usual situation. But with css I don't know, should I test it, or not.
Some articles about RTL tell that we don't have to test css. But
in my opinion, in this case, our css prop is important for end user
(e.g. some other developer who will use this component) and this css
should be tested. What's the right way?

Answer 1

Testing a React Application should be about behaviors. That is, how the application behaves when controlled by an end user. That's one of the guiding principles of react-testing-library, and one I agree with.
Therefore, going by this statement you can do two different things:
Test the complete behavior that causes the border color to change. That is Integration Testing
Type check the component to guarantee that you cannot pass an incorrect value for borderColor. That is Unit Testing
In my opinion with this use case, testing anything else would be testing React itself or, as the other answer noted, you ability to write a correct css string. The later can be tested with your own eyes anyway and isn't likely to change
Type checking example
Giving you an example for integration testing is hard to do without knowing your complete use case. As for type checking you have two options:
Using PropTypes
Switching to Typescript
Note: These options aren't equivalent. Proptypes is a library that checks the props at runtime with a developement build. They are ignored with a production build. Typescript on the other hand is a complete compiler, that runs during the build. The correct solution depends on your setup
With PropTypes
You can use PropTypes.oneOf :
Button.propTypes = {
// Edit as needed
borderColor: PropTypes.oneOf(["red", ,blue"])
}
Typescript
interface ButtonProps {
borderColor: "blue" | "red";
}
const Button: React.FunctionComponent<ButtonProps> = ({borderColor, children}) => {...}

Answer 2

Potentially misreading your question, but maybe you're only asking because "is this string a valid CSS color" feels like a silly or annoying detail to test, even though you're aware of the problems that not writing tests will have on other developers who will use this component.
Is this a silly thing to test? I agree conditionally.
IMO this is far better solved using Typescript to enforce constraints on what form the string can take. Some ideas here: TypeScript - is it possible validate string types based on pattern matching or even length?
A better thing to test is probably a functionality question like "does this component genuinely create a button wrapping the children with the 1px solid borderColor that we asked for?
In that case, yes I'd write a test for that functionality.