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Overview

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formatters.md index.md plugin-testing.md preset-testing.md test-configuration.md utilities.md

tile.json

Preset Testing

Testing functionality specifically designed for Babel presets with preset-specific configuration options.

Capabilities

Preset Configuration

Configuration options for testing Babel presets instead of individual plugins.

interface PluginTesterOptions {
  /** The babel preset under test */
  preset?: (...args: any[]) => Babel.TransformOptions;
  /** Name for the preset (used in test descriptions) */
  presetName?: string;
  /** Options passed to the preset */
  presetOptions?: any;
}

Usage Examples:

import pluginTester from "babel-plugin-tester";
import myPreset from "../my-preset";

// Basic preset testing
pluginTester({
  preset: myPreset,
  presetName: "my-typescript-preset",
  tests: [
    {
      code: `
        interface User {
          name: string;
          age: number;
        }
        const user: User = { name: "John", age: 30 };
      `,
      output: `
        const user = { name: "John", age: 30 };
      `,
    },
  ],
});

// Preset with options
pluginTester({
  preset: myPreset,
  presetName: "react-preset",
  presetOptions: {
    runtime: "automatic",
    development: true,
  },
  tests: [
    {
      code: `
        function App() {
          return <div>Hello World</div>;
        }
      `,
      output: `
        import { jsx as _jsx } from "react/jsx-dev-runtime";
        function App() {
          return _jsx("div", { children: "Hello World" });
        }
      `,
    },
  ],
});

Custom Preset Execution

Special symbol for controlling preset execution context.

/** Symbol to run preset in the current test context */
const runPresetUnderTestHere: unique symbol;

Usage Example:

import { pluginTester, runPresetUnderTestHere } from "babel-plugin-tester";

pluginTester({
  preset: myPreset,
  tests: [
    {
      code: `
        import { runPresetUnderTestHere } from "babel-plugin-tester";
        runPresetUnderTestHere;
        const Component = () => <div>Test</div>;
      `,
      output: `
        const Component = () => React.createElement("div", null, "Test");
      `,
    },
  ],
});

Preset and Plugin Restrictions

Important limitation: cannot test both plugins and presets simultaneously.

// ❌ This will throw an error
pluginTester({
  plugin: myPlugin,
  preset: myPreset, // Error: cannot specify both
  tests: [...]
});

// ✅ Test plugin or preset separately
pluginTester({
  plugin: myPlugin,
  tests: [...]
});

pluginTester({
  preset: myPreset,
  tests: [...]
});

Preset Name Handling

Preset names default to "unknown preset" if not provided and cannot be inferred.

// Explicit preset name
pluginTester({
  preset: myPreset,
  presetName: "my-custom-preset",
  tests: [...]
});

// Will use "unknown preset" as default
pluginTester({
  preset: myPreset,
  tests: [...]
});