# Writing Tests

Testing an app with react-md components should not require many changes to your normal testing flow. The only times weird issues might occur are when using components that rely on one of the providers included by the Configuration component.

This guide will provide a few suggestions for setting up an app with jest and react-testing-library.

# Initializing window.matchMedia

If a component from your app or react-md uses the useAppSize or useMediaQuery hooks, your tests might fail due to window.matchMedia being undefined. In this case, you'll want to create or update a testSetup.ts (or testSetup.js) to include a very simple polyfill.

Edit testSetup.ts:

12345678910111213141516171819+import {
+  DEFAULT_DESKTOP_MIN_WIDTH,
+  DEFAULT_DESKTOP_LARGE_MIN_WIDTH,
+} from '@react-md/utils';
+
+if (typeof window.matchMedia !== 'function') {
+  window.matchMedia = (query) => ({
+    media: query,
+    matches:
+      query.includes(`${DEFAULT_DESKTOP_MIN_WIDTH}`) ||
+      query.includes(`${DEFAULT_DESKTOP_LARGE_MIN_WIDTH}`),
+    onchange: () => {},
+    addListener: () => {},
+    removeListener: () => {},
+    addEventListener: () => {},
+    removeEventListener: () => {},
+    dispatchEvent: () => false,
+  });
+}

Edit jest.config.js:

123456 module.exports = {
   preset: 'ts-jest',
   testEnvironment: 'jsdom',
+  setupFilesAfterEnv: ['<rootDir>/testSetup.ts'],
   // any other config you want
 }

This polyfill will make all your tests run in desktop mode by default.

# Testing different app sizes

Since your layout will most likely change depending on the app size, you'll also need to be able to configure the matches return value on a test-by-test basis. Luckily, this can be easily implemented by using jest.spyOn:

12345678910111213141516171819202122232425import {
  DEFAULT_PHONE_MAX_WIDTH,
  DEFAULT_TABLET_MIN_WIDTH,
  DEFAULT_DESKTOP_MIN_WIDTH,
} from "@react-md/utils";

const MEDIA_DEFAULTS: MediaQueryList = {
  query: "",
  matches: false,
  onchange: () => {},
  addListener: () => {},
  removeListener: () => {},
  addEventListener: () => {},
  removeEventListener: () => {},
  dispatchEvent: () => false,
};

it("should render correctly on mobile", () => {
  const matchMedia = jest.spyOn(window, "matchMedia");
  matchMedia.mockImplementation((query) => ({
    ...MEDIA_DEFAULTS,
    query,
    matches: query.includes(DEFAULT_PHONE_MAX_WIDTH),
  }));
});

# Adding a Configuration Wrapper

Since you'll want your automated tests to reflect your actual browser environment, it is a good idea to always wrap your tests with the same Configuration component used at the root of your app especially if you change up the default icons. If you use react-testing-library this can be done really easily by following the documentation about creating a custom renderer. Here's a very quick example that creates a src/test-utils.tsx that defines the custom renderer and updates the src/components/__tests__/Component.tsx to use the custom renderer.

Create src/test-utils.tsx:

123456789101112131415161718192021222324import {
  render as renderer,
  RenderOptions,
  RenderResult,
} from "@testing-library/react";
import { Configuration, ConfigurationProps } from "@react-md/layout";

export * from "@testing-library/react";

const configuration: ConfigurationProps = {
  // your configuration
};

export function render(
  ui: ReactElement,
  options?: RenderOptions
): RenderResult {
  return renderer(ui, {
    ...options,
    wrapper: ({ children }) => (
      <Configuration {...configuration}>{children}</Configuration>
    ),
  });
}

Edit src/components/__tests__/Component.tsx:

1234-import { render } from "@testing-library/react";
+import { render } from "../../test-utils";

 // your tests