svelte-component-double/index.js

A test double for Svelte 3 components

import ComponentDouble, {
  instanceSelector,
  spySelector,
} from "./lib/ComponentDouble.svelte";

export const componentDouble = (original) => {
  let instances = [];

  const name = original instanceof Function ? original.name : original;
  class TestComponent extends ComponentDouble {
    constructor(options) {
      const { props } = options;
      super({
        ...options,
        props: {
          ...props,
          _spyName: name,
          _spyInstance: instances.length,
        },
      });
      instances.push(this);
    }

    updateBoundValue(component, prop, value) {
      const fnName = `${name.toLowerCase()}_${prop}_binding`;
      const updateFn = component.$$.ctx.find(
        (value) => value instanceof Function && value.name === fnName
      );
      updateFn(value);
    }
  }

  TestComponent.toString = () =>
    original instanceof Function
      ? `${name} component double`
      : `"${name}" component double`;
  TestComponent.instances = instances;
  TestComponent.selector = () => spySelector(name);
  TestComponent.instanceSelector = (instance) =>
    instanceSelector(name, instance);
  TestComponent.findMatching = (matchFn) =>
    instances
      .map((instance) => instance.getNonSpyProps())
      .find((props) => matchFn(props));
  TestComponent.firstInstance = () => instances[0];
  TestComponent.lastInstance = () => instances[instances.length - 1];
  TestComponent.getInstanceFromElement = (domElement) => {
    for (let i = 0; i < instances.length; ++i) {
      if (domElement.matches(TestComponent.instanceSelector(i))) {
        return instances[i];
      }
    }
    throw new Error(
      `${domElement.outerHTML} does not correspond to a ${name} component instance`
    );
  };
  TestComponent.mountedInstances = () =>
    instances.filter((instance) => instance.$$.fragment);
  TestComponent.reset = () => instances.splice(0);
  TestComponent.propsOfAllInstances = () =>
    TestComponent.mountedInstances().map((instance) =>
      instance.getNonSpyProps()
    );
  TestComponent.dispatch = (...args) =>
    TestComponent.lastInstance().dispatch(...args);
  return TestComponent;
};