All files / assert / match.ts

// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
import { AssertionError } from "./assertion_error.ts";

/**
 * Make an assertion that `actual` match RegExp `expected`. If not
 * then throw.
 *
 * @example Usage
 * ```ts ignore
 * import { assertMatch } from "@std/assert";
 *
 * assertMatch("Raptor", /Raptor/); // Doesn't throw
 * assertMatch("Denosaurus", /Raptor/); // Throws
 * ```
 *
 * @param actual The actual value to be matched.
 * @param expected The expected pattern to match.
 * @param msg The optional message to display if the assertion fails.
 */
export function assertMatch(
  actual: string,
  expected: RegExp,
  msg?: string,
) {
  if (expected.test(actual)) return;
  const msgSuffix = msg ? `: ${msg}` : ".";
  msg = `Expected actual: "${actual}" to match: "${expected}"${msgSuffix}`;
  throw new AssertionError(msg);
}