Getting Started

Install

Add as-test to an AssemblyScript project:

npm install --save-dev as-test

as-test is self-contained — value serialization for assertions, snapshots, and log() is built in, so there are no required peer dependencies.

The WASI target additionally needs @assemblyscript/wasi-shim:

npm install --save-dev @assemblyscript/wasi-shim

Scaffold a project

The fastest path is the initializer:

npx ast init

ast init can create:

• as-test.config.json
• runner scripts under .as-test/runners/
• a sample spec in assembly/__tests__/
• an optional sample fuzzer in assembly/__fuzz__/
• assembly/tsconfig.json

Useful flags:

Flag	Effect
--target <wasi|bindings|web>	Set the build target (default wasi).
--example <minimal|full|none>	Choose the sample spec, or skip it.
--fuzz-example / --no-fuzz-example	Include or omit the sample fuzzer.
--enable <list>	Turn on features at scaffold time (e.g. coverage, try-as).
--dir <path>	Scaffold into a specific directory.
--install	Install dependencies after scaffolding.
--yes, -y	Accept defaults; no prompts.
--force	Overwrite managed files.

npx ast init --target bindings --example full --fuzz-example --yes

Your first spec

A spec is any file matched by input (default assembly/__tests__/*.spec.ts). Register suites, assert with expect, and end with run():

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

describe("example", () => {
  test("adds numbers", () => {
    expect(1 + 2).toBe(3);
  });
});

run() is called for you when a spec defines suites but never calls it. Add an explicit run() only when you need to pass RunOptions.

Run the suite

npx ast test            # build + run every spec
npx ast test --parallel # spread files across a worker pool
npx ast fuzz            # run fuzz targets only
npx ast test --fuzz     # run specs, then fuzzers
npx ast test --watch    # re-run on change

ast test compiles each spec with the AssemblyScript compiler (running the as-test transform), then executes the resulting wasm through the configured runtime. See the CLI reference for the full flag set.

Minimal config

ast init writes this for you, but the whole thing fits in a few lines:

{
  "input": ["assembly/__tests__/*.spec.ts"],
  "output": ".as-test/",
  "buildOptions": {
    "target": "wasi"
  },
  "runOptions": {
    "runtime": {
      "cmd": "node ./.as-test/runners/default.wasi.js"
    }
  }
}

Next

• Writing Tests — the full authoring surface.
• Assertions — every matcher.
• Runtimes & Modes — run the same specs on more than one runtime.
• Configuration — every config field.