Using Vitest + Chevrotain

[khill-fbmc]

Just wanted to share a small extension to expect if you are using vitest with your parser.

Expect Extension

// ./tests/toMatchToken.ts
import { tokenMatcher } from "chevrotain";
import type { IToken, TokenType } from "chevrotain";

export function toMatchToken(received: IToken, tokType: TokenType) {
  const pass = tokenMatcher(received, tokType);

  return {
    pass,
    message: () =>
      `expected token "${received.tokenType.name}" to be type "${tokType.name}"`
  };
}

Vitest Setup file

// ./tests/setup.ts
import { expect } from "vitest";
import { toMatchToken } from "./toMatchToken";
expect.extend({ toMatchToken });

Vitest Config

// vite.config.js
/// <reference types="vitest" />
import { defineConfig } from "vite";

export default defineConfig({
  // ...
  test: {
    setupFiles: ["./tests/setup.ts"],
  },
  // ...
});

Usage

// If you have...
const Integer = createToken({
  name: "Integer",
  pattern: /\d+/
});

// Then test with...
expect(tokens[0]).toMatchToken(Integer);