Coverage

Coverage reports which parts of your code the tests actually exercised. as-test instruments source at compile time, records which points executed, and filters the results in the CLI.

Enable it

Per run:

ast test --enable coverage
ast test --enable coverage --show-coverage      # print uncovered points
ast test --enable coverage --show-coverage=all  # expand nested gaps

Or in config:

{ "coverage": true }

"coverage": true is shorthand for { "enabled": true, "mode": "project" }. Use the object form for finer control (Configuration → coverage).

What gets measured

Instrumentation tracks branch-level points, not just lines:

Point type	Covers
Function	function entry
Return	each return value
IfBranch	if / else arms
Loop	for / while / do bodies
Ternary	both arms of ?:
Assignment	assignment right-hand sides
Throw	throw statements

The summary shows per-file percentages; --show-coverage lists the points that never executed so you can see exactly what's untested.

Coverage modes

Mode	Includes
project (default)	your project sources only
all	project sources and dependency sources

{ "coverage": { "enabled": true, "mode": "all" } }

In project mode you can still opt specific dependencies in by package name:

{
  "coverage": {
    "enabled": true,
    "mode": "project",
    "dependencies": ["json-as", "@scope/pkg"]
  }
}

Names work for normal and pnpm installs, and for the ~lib/<pkg> paths AssemblyScript uses internally.

Refining the file set

After mode and dependencies decide the broad set, narrow it further:

Option	Effect
includeSpecs	Include *.spec.ts files (default false).
include	When non-empty, only files matching these globs are eligible.
exclude	Files matching these globs are dropped.

AssemblyScript standard-library files (~lib/array.ts, etc.) are always excluded; third-party packages under ~lib/<pkg>/… are treated as dependencies, not stdlib, so they follow the mode / dependencies rules.

Ignoring individual points

When a point is intentionally untested (an unreachable guard, a debug-only branch), drop it without excluding the whole file:

{
  "coverage": {
    "enabled": true,
    "ignore": {
      "labels": ["Constructor"],
      "names": ["debug*"],
      "locations": ["assembly/legacy.ts:*"],
      "snippets": ["unreachable()"]
    }
  }
}

Rule	Matches a point by
labels	its kind (e.g. Call, Method, Constructor, Property, Function)
names	the symbol name (glob)
locations	file:line:column (glob)
snippets	the trimmed source snippet (glob)

Artifacts

Coverage artifacts are written under coverageDir (default .as-test/coverage), or set it to "none" to skip writing files while still printing the summary.

Related

• Configuration → coverage
• Multiple Runtimes — coverage can be set per mode.