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mithril-jest

Lets Mithril work with Jest.

Rationale

Jest creates textual snapshots of components to make it easy to spot changes. Differences in rendered HTML are printed to the console as diffs, making it easy to accept or reject the new snapshot; see Jest's snapshot release blog post.

mithril-jest installs Jest (which installs Jasmine), so you can use the regular functions describe, expect, toMatchSnapshot and so on.

To get snapshot-ready HTML from Mithril templates, use function tidy (see below).

Installation

npm install --save-dev mithril-jest

You may need to install command line library tidy-html5 too (on a Mac: brew install tidy-html5).

Tests setup

A typical Jest setup is to have a spec file for each page or component - for component component.js you'll have test file component.spec.js. Jest's convention is to put these test files inside directory __tests__/, but there is no specific need to do this; any directory (for example the conventional test) will work.

If your tests live in directory test, add to package.json to the "scripts" entry:

"test": "jest test/**"

Then run:

npm run test

For interactive mode, run:

npm test --watch

API

tidy

Renders a Mithril template to (tidy) HTML so it can be used to call Jest's toMatchSnapshot. This function:

  1. Renders a template to HTML
  2. Formats the HTML so it becomes multi line and indented

Example

import m from "mithril";
import { tidy } from "mithril-jest";

const Page = {
  view: () =>
    m("div", [
      m("h1", "Page"),
      m("a", {
        href: "/home"
      }, "Back")
    ])
};

describe("Page component", () => {
  it("should have a title", () => {
    const cmp = m(Page);
    const html = tidy(cmp);
    expect(html).toMatchSnapshot();
  });
});

This generates a new (or diffs an existing) snapshot.

The rendered HTML can also be used to inspect:

describe("Page component", () => {
  it("title should be h1 with label 'Page'", () => {
    const cmp = m(Page);
    const html = tidy(cmp);
    expect(html).toContain("Page");
  });
});

Signature

tidy(vnodes, htmlTidyOptions) => String

Argument Type Required Description
vnodes Mithril element Yes The vnodes to be rendered.
htmlTidyOptions Object No Overrides the default HTML Tidy configuration options.
Returns String Rendered and tidied HTML String.

Dependencies

Licence

MIT