Test.ts

const esc_red = `\x1b[31m`;
const esc_green = `\x1b[32m`;
const esc_blue = `\x1b[34m`;
const esc_reset = `\x1b[0m`;

/**
 * Signature of the test function passed to the `test` funciton
 */
export type TestFn = () => void | Promise<void>;
type TestObject = { name: string; fn: TestFn };
type TestArray = Array<TestObject>;

const tests: TestArray = [];

/**
 * Register `test_fn` in the test system associated with the `name`
 */
export function test(name: string, test_fn: TestFn) {
  tests.push({ name, fn: test_fn });
}

/**
 * Asserts the condition helping controll flow analysis and type narrowing
 * If `cond` is falsy throws error with `msg`
 */
export function assert(cond: unknown, msg = ""): asserts cond {
  if (!cond) throw `  - Assertion failed${msg ? `: ${msg}` : ``}`;
}


/**
 * Asserts `a` equals `b`
 * Do not act on controll flow analysis
 * In case `a != b` throws an error with `msg`
 */
export function assert_equals(a: unknown, b: unknown, msg?: string) {
  const ok =
    typeof a === "number" && typeof b === "number"
      ? Object.is(a, b)
      : JSON.stringify(a) === JSON.stringify(b);

  if (!ok) {
    throw `  - Assertion failed: ${msg ??
      `\n  - expected: ${esc_green}${JSON.stringify(b)}${esc_reset}\n  - received: ${esc_red}${JSON.stringify(a)}${esc_reset}`}`
  }
}

/**
 * Runs registered tests
 */
export async function run_tests(): Promise<void> {
  const failed: Array<string> = [];

  console.log(`\n${esc_blue}[ Test Runner ]${esc_reset}\n`);

  for (const { name, fn } of tests) {
    try {
      await fn();
      console.log(`${esc_green}✓${esc_reset} ${name}`);
    } catch (e) {
      failed.push(name);
      console.error(`${esc_red}✗${esc_reset} ${name}`);
      console.error(e);
    }
  }

  if (failed.length > 0) {
    console.error(`\n${failed.length}/${tests.length} test(s) failed\n`);
    for(const f of failed) {
      console.error(`- ${esc_red}"${f}"${esc_reset} failed`);
    }
    console.log("");
    throw "TestFailed";
  }
  else console.log(`\nAll ${tests.length} tests passed`);
}