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

pnpm add @udecode/plate-test-utils

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 to set up the editor
  4. Apply the transform(s) directly
  5. Assert the editor's new state

Example testing bold formatting:

it('should apply bold formatting', () => {
  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 = createPlateEditor({
    plugins: [BoldPlugin],
    value: input.children,
    selection: input.selection,
  });
 
  // Apply transform directly
  editor.tf.toggleMark('bold');
 
  expect(editor.children).toEqual(output.children);
});

Testing Selection

Test how operations affect the editor's selection:

it('should collapse selection on backspace', () => {
  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 = createPlateEditor({
    value: input.children,
    selection: input.selection,
  });
 
  editor.tf.deleteBackward();
 
  expect(editor.children).toEqual(output.children);
  expect(editor.selection).toEqual(output.selection);
});

Testing Key Events

When you need to test keyboard handlers directly:

it('should call the onKeyDown handler', () => {
  const input = (
    <editor>
      <hp>
        Hello <anchor />world<focus />
      </hp>
    </editor>
  ) as any as PlateEditor;
 
  // Create a mock handler to verify it's called
  const onKeyDownMock = jest.fn();
 
  const editor = createPlateEditor({
    value: input.children,
    selection: input.selection,
    plugins: [
      {
        key: 'test',
        handlers: {
          onKeyDown: onKeyDownMock,
        },
      },
    ],
  });
 
  // Create the keyboard event
  const event = new KeyboardEvent('keydown', {
    key: 'Enter',
  }) as any;
 
  // Call the handler directly
  editor.plugins.test.handlers.onKeyDown({
    ...getEditorPlugin(editor, { key: 'test' }),
    event,
  });
 
  // Verify the handler was called
  expect(onKeyDownMock).toHaveBeenCalled();
});

Testing Complex Scenarios

For complex plugins like tables, test various scenarios by directly applying transforms:

describe('Table plugin', () => {
  it('should insert a table', () => {
    const input = (
      <editor>
        <hp>
          Test<cursor />
        </hp>
      </editor>
    ) as any as PlateEditor;
 
    const output = (
      <editor>
        <hp>Test</hp>
        <htable>
          <htr>
            <htd>
              <hp>
                <cursor />
              </hp>
            </htd>
            <htd>
              <hp></hp>
            </htd>
          </htr>
          <htr>
            <htd>
              <hp></hp>
            </htd>
            <htd>
              <hp></hp>
            </htd>
          </htr>
        </htable>
      </editor>
    ) as any as PlateEditor;
 
    const editor = createPlateEditor({
      value: input.children,
      selection: input.selection,
      plugins: [TablePlugin],
    });
 
    // Call transform directly
    editor.tf.insertTable({ rows: 2, columns: 2 });
 
    expect(editor.children).toEqual(output.children);
    expect(editor.selection).toEqual(output.selection);
  });
});

Testing Plugins with Options

Test how different plugin options affect behavior:

describe('when undo is enabled', () => {
  it('should undo text format upon delete', () => {
    const input = (
      <fragment>
        <hp>
          1/<cursor />
        </hp>
      </fragment>
    ) as any;
 
    const output = (
      <fragment>
        <hp>
          1/4<cursor />
        </hp>
      </fragment>
    ) as any;
 
    const editor = createPlateEditor({
      plugins: [
        AutoformatPlugin.configure({
          options: {
            enableUndoOnDelete: true,
            rules: [
              {
                format: '¼',
                match: '1/4',
                mode: 'text',
              },
            ],
          },
        }),
      ],
      value: input,
    });
 
    // Trigger the autoformat
    editor.tf.insertText('4');
 
    // Simulate backspace key
    const event = new KeyboardEvent('keydown', {
      key: 'backspace',
    }) as any;
 
    // Call the handler
    editor.plugins[AutoformatPlugin.key].handlers.onKeyDown({
      ...getEditorPlugin(editor, AutoformatPlugin),
      event,
    });
 
    // With enableUndoOnDelete: true, pressing backspace should restore the original text
    expect(input.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