Unit Testing Plate

Learn how to unit test Plate editor and plugins.

This guide outlines best practices for unit testing Plate plugins and components using @udecode/plate-test-utils.

Installation

npm install @udecode/plate-test-utils slate-hyperscript

Setting Up Tests

Add the JSX pragma at the top of your test file:

/** @jsx jsx */
 
import { jsx } from '@udecode/plate-test-utils';
 
jsx; // so ESLint doesn't complain

This allows you to use JSX syntax for creating editor values.

Creating Test Cases

Editor State Representation

Use JSX to represent editor states:

const input = (
  <editor>
    <hp>
      Hello<cursor /> world
    </hp>
  </editor>
) as any as PlateEditor;

Node elements like <hp />, <hul />, <hli /> represent different types of nodes.

Special elements like <cursor />, <anchor />, and <focus /> represent selection states.

Testing Transforms

  1. Create an input state
  2. Define the expected output state
  3. Use createPlateEditor or createPlateTestEditor to set up the editor
  4. Apply the transform(s)
  5. Assert the editor's new state

Example testing bold formatting:

it('should use custom hotkey for bold', async () => {
  const input = (
    <editor>
      <hp>
        Hello <anchor />
        world
        <focus />
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const output = (
    <editor>
      <hp>
        Hello <htext bold>world</htext>
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const [editor, { triggerKeyboardEvent }] = await createPlateTestEditor({
    editor: input,
    plugins: [
      BoldPlugin.configure({
        handlers: {
          onKeyDown: ({ editor, event }) => {
            if (event.key === 'b' && event.ctrlKey) {
              editor.tf.toggle.mark({ key: 'bold' });
            }
          },
        },
      }),
    ],
  });
 
  await triggerKeyboardEvent('mod+b');
 
  expect(editor.children).toEqual(output.children);
});

Testing Selection

Test how operations affect the editor's selection:

it('should collapse selection on backspace', async () => {
  const input = (
    <editor>
      <hp>
        He<anchor />llo wor<focus />ld
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const output = (
    <editor>
      <hp>
        He<cursor />ld
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const [editor] = await createPlateTestEditor({
    editor: input,
  });
 
  editor.deleteBackward('character');
 
  expect(editor.children).toEqual(output.children);
  expect(editor.selection).toEqual(output.selection);
});

Testing Key Events

Use triggerKeyboardEvent from createPlateTestEditor:

it('should extend selection on shift+ArrowRight', async () => {
  const input = (
    <editor>
      <hp>
        Hello <cursor />world
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const output = (
    <editor>
      <hp>
        Hello <anchor />wor<focus />ld
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const [editor, { triggerKeyboardEvent }] = await createPlateTestEditor({
    editor: input,
  });
 
  await triggerKeyboardEvent('shift+ArrowRight');
  await triggerKeyboardEvent('shift+ArrowRight');
  await triggerKeyboardEvent('shift+ArrowRight');
 
  expect(editor.selection).toEqual(output.selection);
});

Testing Complex Scenarios

For complex plugins like tables, test various scenarios:

describe('Table plugin', () => {
  it('should add a row below on Tab in last cell', async () => {
    const input = (
      <editor>
        <htable>
          <htr>
            <htd>Cell 1</htd>
            <htd>
              Cell 2<cursor />
            </htd>
          </htr>
        </htable>
      </editor>
    ) as any as PlateEditor;
 
    const output = (
      <editor>
        <htable>
          <htr>
            <htd>Cell 1</htd>
            <htd>Cell 2</htd>
          </htr>
          <htr>
            <htd>
              <cursor />
            </htd>
            <htd></htd>
          </htr>
        </htable>
      </editor>
    ) as any as PlateEditor;
 
    const [editor, { triggerKeyboardEvent }] = await createPlateTestEditor({
      editor: input,
      plugins: [TablePlugin],
    });
 
    await triggerKeyboardEvent('Tab');
 
    expect(editor.children).toEqual(output.children);
    expect(editor.selection).toEqual(output.selection);
  });
});

Testing Plugins with Options

Test how different plugin options affect behavior:

it('should use custom hotkey for bold', async () => {
  const handler = jest.fn();
  
  const input = (
    <editor>
      <hp>
        Hello <cursor />world
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const output = (
    <editor>
      <hp>
        Hello <htext bold>world</htext>
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  const [editor, { triggerKeyboardEvent }] = await createPlateTestEditor({
    editor: input,
    plugins: [
      BoldPlugin.configure({
        shortcuts: {
          toggleBold: {
            handler,
            keys: 'mod+shift+b',
          },
        },
      }),
    ],
  });
 
  await triggerKeyboardEvent('mod+shift+b');
 
  expect(editor.children).toEqual(output.children);
});

Mocking vs. Real Transforms

While mocking can be useful for isolating specific behaviors, Plate tests often assess actual editor children and selection after transforms. This approach ensures that plugins work correctly with the entire editor state.

DebuggingPlaywright Testing