std/assert/less.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { format } from "@std/internal/format";
import { AssertionError } from "./assertion_error.ts";

/**
 * Make an assertion that `actual` is less than `expected`.
 * If not then throw.
 *
 * @example Usage
 * ```ts ignore
 * import { assertLess } from "@std/assert";
 *
 * assertLess(1, 2); // Doesn't throw
 * assertLess(2, 1); // Throws
 * ```
 *
 * @typeParam T The type of the values to compare.
 * @param actual The actual value to compare.
 * @param expected The expected value to compare.
 * @param msg The optional message to display if the assertion fails.
 */
export function assertLess<T>(actual: T, expected: T, msg?: string) {
  if (actual < expected) return;

  const actualString = format(actual);
  const expectedString = format(expected);
  throw new AssertionError(msg ?? `Expect ${actualString} < ${expectedString}`);
}