An Item component to be tested and the accompanying unit test suite for that component.

Item.js

import React from "react";
import Link from "next/link";
import PropTypes from "prop-types";
import formatMoney from "../lib/formatMoney";
import Title from "../components/styles/Title";
import ItemStyles from "../components/styles/ItemStyles";
import PriceTag from "../components/styles/PriceTag";
import DeleteItem from "../components/DeleteItem";
import AddToCart from "../components/AddToCart";

export default class Item extends React.Component {
  static propTypes = {
    item: PropTypes.shape({
      id: PropTypes.string.isRequired,
      title: PropTypes.string.isRequired,
      price: PropTypes.number.isRequired,
      description: PropTypes.string.isRequired,
      image: PropTypes.string,
      largeImage: PropTypes.string
    })
  };

  render() {
    const { item } = this.props;
    return (
      <ItemStyles>
        {item.image && <img src={item.image} alt={item.title} />}
        <Title>
          <Link
            href={{
              pathname: "/item",
              query: { id: item.id }
            }}
          >
            <a>{item.title}</a>
          </Link>
        </Title>
        <PriceTag>{formatMoney(item.price)}</PriceTag>
        <p>{item.description}</p>

        <div className="buttonList">
          <Link
            href={{
              pathname: "update",
              query: { id: item.id }
            }}
          >
            <a>Edit</a>
          </Link>
          <AddToCart id={item.id} />
          <DeleteItem id={item.id}>Delete This Thing</DeleteItem>
        </div>
      </ItemStyles>
    );
  }
}

Item.test.js

describe("<Item />", () => {
  test.todo('it always renders `ItemStyles`')
  describe("the rendered `ItemStyles`", () => {
    test.todo("wraps all other elements");
    // I can't find a way to confirm there aren't any sibling elements to ItemStyles

    describe("when `item.image` is defined", () => {
      beforeEach(() => {
        props.image = "someimage.jpg";
      });

      test.todo("it renders an `img` tag");
      test.todo("it sets the rendered `img` `src` to `item.image`");
      test.todo("it sets the rendered `img` `alt` to `item.title`");
    });

    describe("when `item.image` is not defined", () => {
      test.todo("it does not render an `img` tag");
    });

    test.todo("always renders a `Title`");
    describe("rendered `Title`", () => {
      test.todo("always renders a `Link`");
      describe("rendered `Link`", () => {
        test.todo("it receives the correct href prop");
        // I hate this. I'm trying to verify that Link received <a>{item.title}</a> as children. Testing what Link does with the passed children is the job Link.test.js, not Item.test.js.
        test.todo("the inner html is `<a>{item.title}</a>`");
      });
    });
    
    test.todo("always renders `PriceTag`");
    describe("rendered `PriceTag`", () => {
      // Same issue as before. This is not the place to be testing the output of PriceTag, even if I know what it should be.
      todo.test("the inner html is `{formatMoney(item.price)}`");
    });

    test.todo("always renders a `p` tag");
    describe("rendered `p` tag", () => {
      test.todo("it is equal to the item description");
    });

    test.todo("always renders a `div.buttonList`");
    describe("rendered `.buttonList`", () => {
      test.todo("always renders a `Link`");
      describe("rendered `Link`", () => {
        test.todo("it receives the correct href prop");
        test.todo("the inner text is `Edit`");
      });

      test.todo("always renders an `AddToCart`");
      describe("rendered `AddToCart`", () => {
        test.todo(
          "sets the rendered `AddToCart`'s `id` prop to the same value as `item.id` "
        );
      });

      test.todo("always renders an `DeleteItem`");
      describe("rendered `DeleteItem`", () => {
        test.todo(
          "sets the rendered `DeleteItem`'s `id` prop to the same value as `item.id` "
        );
        test.todo("has innertext that equals `Delete This Thing`");
      });
    });
  });
});