silphius/app/swcx/evaluators/update.test.js

import {expect, test} from 'vitest';

import evaluate from '@/swcx/evaluate.js';
import expression from '@/swcx/test/expression.js';

const scopeTest = test.extend({
  scope: async ({}, use) => {
    await use({
      S: {O: {}},
      get(k) { return this.S[k]; },
      set(k, v) { return this.S[k] = v; }
    });
  },
});

scopeTest('evaluates postfix updates', async ({scope}) => {
  scope.set('x', 4);
  let evaluated = evaluate(await expression('y = x++'), {scope});
  expect(evaluated.value)
    .to.equal(4);
  expect(scope.get('x'))
    .to.equal(5);
  expect(scope.get('y'))
    .to.equal(4);
  evaluated = evaluate(await expression('y = x--'), {scope});
  expect(evaluated.value)
    .to.equal(5);
  expect(scope.get('x'))
    .to.equal(4);
  expect(scope.get('y'))
    .to.equal(5);
});

scopeTest('evaluates prefix updates', async ({scope}) => {
  scope.set('x', 4);
  let evaluated = evaluate(await expression('y = ++x'), {scope});
  expect(evaluated.value)
    .to.equal(5);
  expect(scope.get('x'))
    .to.equal(5);
  expect(scope.get('y'))
    .to.equal(5);
  evaluated = evaluate(await expression('y = --x'), {scope});
  expect(evaluated.value)
    .to.equal(4);
  expect(scope.get('x'))
    .to.equal(4);
  expect(scope.get('y'))
    .to.equal(4);
});