Assertions

Assertions start from expect(value, message?, location?).

Basic example:

import { expect, test } from "as-test";

test("example", () => {
  expect(1 + 2).toBe(3);
  expect("hello").toStartWith("he");
  expect([1, 2, 3]).toContain(2);
});

Negation

Use .not before a matcher:

expect(1).not.toBe(2);
expect("hello").not.toEndWith("xx");

Messages

The optional second argument becomes the failure message when the matcher fails:

expect(total, "sum should stay stable").toBe(42);

Matcher Groups

• Equality
• Numbers
• Types And Truthiness
• Strings And Collections
• Snapshots And Throws

Fuzzing Interaction

Inside a fuzzer:

• failed expect(...) calls fail the current fuzz iteration
• they are counted in the fuzz result, not the normal test totals
• the first failure details are recorded in the fuzz report

See Fuzzing for how failures and repro commands are reported.