Environment

• Dart SDK 3.12.2 stable on macOS arm64
• macOS 26.5.2 (25F84)
• test 1.31.0

Problem

During dart test, the dart_test.kernel.* temporary directory retains a complete .dill file for every test file. Temporary disk usage grows approximately linearly with the number of test files and is released only when the full command exits.

name: dart_test_kernel_retention_repro
publish_to: none

environment:
  sdk: ^3.12.0

dev_dependencies:
  analyzer: 12.0.0
  test: 1.31.0

Create tool/case_test.dart:

import 'package:analyzer/dart/analysis/utilities.dart';
import 'package:test/test.dart';

void main() {
  test('parses a Dart library', () {
    final result = parseString(
      content: 'class Example { final int value = 1; }',
    );
    expect(result.errors, isEmpty);
  });
}

Copy it into 40 test files:

mkdir -p test
for index in $(seq -w 1 40); do
  cp tool/case_test.dart "test/case_${index}_test.dart"
done

Add test/zz_hold_test.dart to keep the process open long enough to inspect its temporary directory:

import 'dart:async';
import 'package:test/test.dart';

void main() {
  test('hold', () => Future<void>.delayed(const Duration(seconds: 30)));
}

Run:

dart pub get
mkdir -p .tmp
TMPDIR="$PWD/.tmp" dart test

While the hold test is running, inspect the directory from another terminal:

find .tmp -name 'test.dart_*.dill' | wc -l
du -sh .tmp/dart_test.kernel.*

Expected behavior

Temporary disk usage should remain bounded as test files finish.

Actual behavior

The reproduction retains 41 .dill files and uses approximately 950 MB. Each ordinary test file adds approximately 23 MB, although the 40 copied test files contain only about 11 KB of source in total.

In a larger run with 274 test files, the temporary directory exceeded 10 GB and exhausted the available disk space before the command completed.

--verbose output

When the disk filled, the remaining test files failed to load with:

FileSystemException: writeFrom failed, path = '.../dart_test.kernel.<suffix>/output.dill' (OS Error: No space left on device, errno = 28)