Configuration

Configuration lives in as-test.config.json. The bundled JSON Schema (as-test.config.schema.json) powers editor autocompletion — reference it with $schema:

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

Top-level fields

Field	Type	Default	Purpose
input	string[]	["./assembly/__tests__/*.spec.ts"]	Globs for spec files. Negate with !.
output	string | object	—	Output location (alias).
outDir	string	./.as-test/build	Compiled artifacts.
logs	string | "none"	./.as-test/logs	Captured log() output, or "none".
coverageDir	string | "none"	./.as-test/coverage	Coverage artifacts, or "none".
snapshotDir	string	./.as-test/snapshots	Stored snapshots.
coverage	boolean | object	false	Coverage settings.
features	string[]	[]	Enabled features.
env	string | string[] | object	{}	Environment values.
buildOptions	object	—	Build options.
runOptions	object	—	Run options.
fuzz	object	—	Fuzz config.
modes	object	{}	Named modes.
config	string	"none"	Optional asconfig path passed to asc.

Output paths

output is a convenience alias. Use a single string for the root, or an object to place each artifact kind:

{ "output": ".as-test/" }

{
  "output": {
    "build": "./.as-test/build",
    "logs": "./.as-test/logs",
    "coverage": "./.as-test/coverage",
    "snapshots": "./.as-test/snapshots"
  }
}

The explicit fields (outDir, logs, coverageDir, snapshotDir) still work and override the alias when both are set. ast clean removes build, logs, and coverage from these locations (and the shared fuzz.crashDir).

Environment values

env, buildOptions.env, and runOptions.env each accept three forms:

• a .env file path,
• an array of KEY=value strings,
• an object map.

{ "env": { "LOG_LEVEL": "debug" } }

They merge together — top-level first, then build/run-specific, then mode overrides on top.

Build options

{
  "buildOptions": {
    "target": "wasi",
    "args": [],
    "cmd": "",
    "env": {}
  }
}

Field	Type	Purpose
target	"wasi" | "bindings" | "web"	Build target (see Targets & Runtimes).
args	string[]	Extra arguments passed to asc.
cmd	string	Replace the default build command entirely.
env	env	Build-only environment overrides.

buildOptions.cmd supports the placeholders <file>, <name>, <outFile>, <target>, and <mode>.

For bindings/web targets, as-test injects --bindings raw unless you declare --bindings yourself in args (or in a referenced asconfig). See Bindings: raw & esm.

Run options

{
  "runOptions": {
    "runtime": {
      "cmd": "node ./.as-test/runners/default.wasi.js",
      "browser": ""
    },
    "reporter": "default",
    "env": {}
  }
}

Field	Type	Purpose
runtime.cmd	string	Runtime command. Supports <file> and <name>.
runtime.browser	string	Browser for web targets: chrome, chromium, firefox, webkit, or a path.
reporter	string | object	Reporter selection.
env	env	Run-only environment overrides.

The generated runners are env-driven single-file scripts, so standard runner commands don't need a <file> argument. Reporter accepts "", "default", "tap", a custom module path, or an object — see Reporters.

Coverage

Boolean shorthand or a detailed object:

{
  "coverage": {
    "enabled": true,
    "mode": "project",
    "dependencies": ["json-as"],
    "includeSpecs": false,
    "include": [],
    "exclude": [],
    "ignore": { "labels": [], "names": [], "locations": [], "snippets": [] }
  }
}

Field	Default	Purpose
enabled	false	Turn coverage on. "coverage": true is shorthand for { enabled: true, mode: "project" }.
mode	"project"	project = your sources only; all = include dependencies.
dependencies	[]	Package-name allowlist for dependency coverage.
includeSpecs	false	Include *.spec.ts files.
include / exclude	[]	Glob refinements applied after the above.
ignore	—	Drop points by labels, names, locations, or snippets.

See Coverage for details.

Fuzz

Used by ast fuzz and ast test --fuzz:

{
  "fuzz": {
    "input": ["./assembly/__fuzz__/*.fuzz.ts"],
    "runs": 1000,
    "maxInputBytes": 4096,
    "target": "bindings",
    "corpusDir": "./.as-test/fuzz/corpus",
    "crashDir": "./.as-test/crashes"
  }
}

Field	Default	Purpose
input	["./assembly/__fuzz__/*.fuzz.ts"]	Globs for fuzz targets.
runs	1000	Iterations per target.
seed	random	Base seed; omit for a fresh random seed each run.
maxInputBytes	4096	Max generated input size.
target	"bindings"	Fuzz builds require the bindings target.
corpusDir	./.as-test/fuzz/corpus	Seed corpus.
crashDir	./.as-test/crashes	Crash artifacts.

Features

features enables compiler-level capabilities:

{ "features": ["try-as"] }

• "try-as" wires up the try-as transform — required for try/catch/finally and the toThrow matcher.
• Other names (e.g. "simd", "threads") are passed to asc as --enable <name>.

CLI --enable / --disable override the config list. In a mode, features replaces the base list entirely — set "features": [] to disable everything for that mode.

Modes

Modes let one project run against multiple targets or runtime commands. Each entry overrides the base config; a value can be an inline object or a string path to an external config file.

{
  "modes": {
    "node:wasi": {
      "buildOptions": { "target": "wasi" },
      "runOptions": { "runtime": { "cmd": "node ./.as-test/runners/default.wasi.js" } }
    },
    "node:bindings": {
      "buildOptions": { "target": "bindings" },
      "runOptions": { "runtime": { "cmd": "node ./.as-test/runners/default.bindings.js" } }
    },
    "chromium:headless": {
      "default": false,
      "buildOptions": { "target": "web" },
      "runOptions": {
        "runtime": {
          "cmd": "node ./.as-test/runners/default.web.js --headless",
          "browser": "chromium"
        }
      }
    }
  }
}

A mode can override input, output directories, coverage, features, fuzz, buildOptions, runOptions, and env.

• "default": false makes a mode manual-only — skipped on a bare ast test, runnable via --mode.
• When any modes are declared, an implicit ast test runs only those modes; the unnamed base config is not added on top. With no modes, the base config runs by itself.
• When multiple modes are active, output paths are namespaced by mode.
• ast clean cleans every configured mode when --mode is omitted, regardless of default.

See Multiple Runtimes for the conceptual guide.