styled-components/test-utils/index.js

// @flow

function assertElement(element) {
  if (!(element instanceof HTMLElement)) {
    throw new Error('Must pass a DOM element to find/findAll(element, styledComponent)"');
  }
}

function assertStyledComponent(styledComponent) {
  if (
    !(styledComponent.styledComponentId && typeof styledComponent.styledComponentId === 'string')
  ) {
    throw new Error('Must pass a styled component to find/findAll(element, styledComponent)"');
  }
}

function find(element /* : Element */, styledComponent /* : Object */) {
  assertElement(element);
  assertStyledComponent(styledComponent);
  return element.querySelector(`.${styledComponent.styledComponentId}`);
}

function findAll(element /* : Element */, styledComponent /* : Object */) {
  assertElement(element);
  assertStyledComponent(styledComponent);
  return element.querySelectorAll(`.${styledComponent.styledComponentId}`);
}

exports.find = find;
exports.findAll = findAll;