flutter channel master && flutter upgrade
./reproduce.sh

#!/usr/bin/env bash
#
# Repro for: `flutter test` intermittently throws
#
#     Exception: Asset 'shaders/ink_sparkle.frag' not found
#
# on the Flutter *master* channel when more than one `flutter test` runs
# concurrently in the same project directory. `stable`/`beta` are unaffected,
# and `flutter test -j 1` always passes.
#
# This script is fully self-contained: it generates a minimal Flutter package
# with many test files and then runs several `flutter test` invocations,
# staggered so that a later invocation rebuilds the shared asset bundle while
# an earlier invocation is still reading the shader from it.
#
# Usage:
#     flutter channel master && flutter upgrade   # once
#     ./reproduce.sh
#
# Tunables (env vars):
#     NUM_TEST_FILES   number of generated test files (default 32)
#     FLUTTER          flutter executable to use      (default "flutter")
#
set -euo pipefail

NUM_TEST_FILES="${NUM_TEST_FILES:-32}"
FLUTTER="${FLUTTER:-flutter}"
PROJECT_DIR="$(mktemp -d)/ink_sparkle_repro"
LOG_DIR="$(mktemp -d)"

echo "Flutter:"
"$FLUTTER" --version | sed 's/^/    /'
echo

# ---------------------------------------------------------------------------
# 1. Generate a minimal Flutter package with many test files.
#    Each test taps a Material button. The default test platform is Android, so
#    Material uses the InkSparkle splash, which lazily loads
#    shaders/ink_sparkle.frag on the first tap.
# ---------------------------------------------------------------------------
mkdir -p "$PROJECT_DIR/test"

cat > "$PROJECT_DIR/pubspec.yaml" <<'YAML'
name: ink_sparkle_repro
description: Minimal repro for flaky ink_sparkle.frag asset serving.
publish_to: none
environment:
  sdk: ">=3.5.0 <4.0.0"
dependencies:
  flutter:
    sdk: flutter
dev_dependencies:
  flutter_test:
    sdk: flutter
flutter:
  uses-material-design: true
YAML

for i in $(seq -w 1 "$NUM_TEST_FILES"); do
  cat > "$PROJECT_DIR/test/tap_${i}_test.dart" <<DART
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('tap a Material button #$i', (tester) async {
    await tester.pumpWidget(const MaterialApp(home: _ButtonPage()));
    // Several taps to widen the window in which the shader is read from disk.
    for (var n = 0; n < 5; n++) {
      await tester.tap(find.byType(ElevatedButton));
      await tester.pump(const Duration(milliseconds: 50));
    }
    await tester.pumpAndSettle();
  });
}

class _ButtonPage extends StatelessWidget {
  const _ButtonPage();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: ElevatedButton(onPressed: () {}, child: const Text('tap')),
      ),
    );
  }
}
DART
done

cd "$PROJECT_DIR"
echo "Generated $NUM_TEST_FILES test files in $PROJECT_DIR"
"$FLUTTER" pub get > /dev/null
echo

# ---------------------------------------------------------------------------
# 2. Run several `flutter test` invocations in the same directory, staggered.
#    On master each invocation unconditionally rebuilds build/unit_test_assets
#    (delete + rewrite). A later invocation's delete therefore lands while an
#    earlier invocation's flutter_tester processes are reading the shader.
# ---------------------------------------------------------------------------
echo "Running 4 staggered, concurrent 'flutter test' invocations..."
"$FLUTTER" test > "$LOG_DIR/run_A.log" 2>&1 &
sleep 4; "$FLUTTER" test > "$LOG_DIR/run_B.log" 2>&1 &
sleep 2; "$FLUTTER" test > "$LOG_DIR/run_C.log" 2>&1 &
sleep 2; "$FLUTTER" test > "$LOG_DIR/run_D.log" 2>&1 &
wait

# ---------------------------------------------------------------------------
# 3. Report.
# ---------------------------------------------------------------------------
NEEDLE="shaders/ink_sparkle.frag' not found"
TOTAL=0
for f in "$LOG_DIR"/run_*.log; do
  c=$(grep -c "$NEEDLE" "$f" || true)
  TOTAL=$((TOTAL + c))
  printf '    %s: %s "Asset not found" failures\n' "$(basename "$f")" "$c"
done

echo
if [ "$TOTAL" -gt 0 ]; then
  echo "REPRODUCED: $TOTAL \"Asset 'shaders/ink_sparkle.frag' not found\" failures."
  echo
  echo "Example stack trace:"
  { grep -A6 "$NEEDLE" "$LOG_DIR"/run_*.log || true; } | head -8 | sed 's/^/    /' || true
  echo
  echo "For comparison, this is always green:"
  echo "    cd $PROJECT_DIR && $FLUTTER test -j 1"
  exit 0
else
  echo "Not reproduced this run (it is timing-dependent)."
  echo "Re-run, or increase NUM_TEST_FILES (e.g. NUM_TEST_FILES=64 ./reproduce.sh)."
  echo "Slower / many-core machines and CI reproduce it most reliably."
  exit 1
fi