Fix SkiaException -> TestFailure, add tests. (#163054)

Fixes https://github.com/flutter/flutter/issues/163051, mitigates
https://github.com/flutter/flutter/issues/162362.

dev/tools/android_driver_extensions/lib/skia_gold.dart

@@ -13,9 +13,11 @@ import 'dart:typed_data';
 
 import 'package:file/local.dart';
 import 'package:flutter_goldens/skia_client.dart';
+import 'package:meta/meta.dart';
 import 'package:path/path.dart' as path;
 import 'package:platform/platform.dart';
 import 'package:process/process.dart';
+import 'package:test_api/test_api.dart';
 
 import 'native_driver.dart';
 
@@ -69,16 +71,30 @@ Future<void> enableSkiaGoldComparator({String? namePrefix}) async {
     httpClient: io.HttpClient(),
     log: io.stderr.writeln,
   );
-  await skiaGoldClient.auth();
-  goldenFileComparator = _GoldenFileComparator(
+  await enableSkiaGoldComparatorForTesting(
     skiaGoldClient,
     namePrefix: namePrefix,
-    isPresubmit: isPresubmit,
+    presubmit: isPresubmit,
   );
 }
 
-final class _GoldenFileComparator extends GoldenFileComparator {
-  _GoldenFileComparator(this.skiaClient, {required this.isPresubmit, this.namePrefix, Uri? baseDir})
+/// Configures [goldenFileComparator] to use Skia Gold (for unit testing).
+@visibleForTesting
+Future<void> enableSkiaGoldComparatorForTesting(
+  SkiaGoldClient skiaGoldClient, {
+  required bool presubmit,
+  String? namePrefix,
+}) async {
+  await skiaGoldClient.auth();
+  goldenFileComparator = _SkiaGoldComparator(
+    skiaGoldClient,
+    namePrefix: namePrefix,
+    isPresubmit: presubmit,
+  );
+}
+
+final class _SkiaGoldComparator extends GoldenFileComparator {
+  _SkiaGoldComparator(this.skiaClient, {required this.isPresubmit, this.namePrefix, Uri? baseDir})
     : baseDir = baseDir ?? Uri.parse(path.dirname(io.Platform.script.path));
 
   final Uri baseDir;
@@ -108,8 +124,18 @@ final class _GoldenFileComparator extends GoldenFileComparator {
         io.stderr.writeln('Skia Gold comparison succeeded comparing "$golden".');
       }
       return true;
-    } else {
-      return skiaClient.imgtestAdd(golden.path, _localFs.file(goldenFile.path));
+    }
+
+    try {
+      return await skiaClient.imgtestAdd(golden.path, _localFs.file(goldenFile.path));
+    } on SkiaException catch (e) {
+      // Convert SkiaException -> TestFailure so that this class implements the
+      // contract of GoldenFileComparator, and matchesGoldenFile() converts the
+      // TestFailure into a standard reported test error (with a better stack
+      // trace, for example).
+      //
+      // https://github.com/flutter/flutter/issues/162621
+      throw TestFailure('$e');
     }
   }
 

dev/tools/android_driver_extensions/test/matches_golden_file_test.dart

@@ -0,0 +1,58 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:typed_data';
+
+import 'package:android_driver_extensions/native_driver.dart';
+// Similar to `flutter_test`, we ignore the implementation import.
+// ignore: implementation_imports
+import 'package:matcher/src/expect/async_matcher.dart';
+import 'package:test/fake.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('passes when the comparator passes', () async {
+    goldenFileComparator = _FakeGoldenFileComparator(_CannedComparisonMode.alwaysPass);
+    final AsyncMatcher matcher = matchesGoldenFile('test');
+    await expectLater(matcher.matchAsync(Uint8List(0)), completion(isNull));
+  });
+
+  test('fails with a default message when the comparator fails', () async {
+    goldenFileComparator = _FakeGoldenFileComparator(_CannedComparisonMode.alwaysFail);
+    final AsyncMatcher matcher = matchesGoldenFile('test');
+    await expectLater(matcher.matchAsync(Uint8List(0)), completion(contains('does not match')));
+  });
+
+  test('fails when the comparator throws a TestFailure', () async {
+    goldenFileComparator = _FakeGoldenFileComparator(_CannedComparisonMode.alwaysThrowTestFailure);
+    final AsyncMatcher matcher = matchesGoldenFile('test');
+    await expectLater(matcher.matchAsync(Uint8List(0)), completion(contains('An expected error')));
+  });
+
+  test('unhandled exception when the comparator throws anything but TestFailure', () async {
+    goldenFileComparator = _FakeGoldenFileComparator(_CannedComparisonMode.alwaysThrowStateError);
+    final AsyncMatcher matcher = matchesGoldenFile('test');
+    await expectLater(matcher.matchAsync(Uint8List(0)), throwsStateError);
+  });
+}
+
+final class _FakeGoldenFileComparator extends Fake implements GoldenFileComparator {
+  _FakeGoldenFileComparator(this._mode);
+  final _CannedComparisonMode _mode;
+
+  @override
+  Future<bool> compare(Uint8List imageBytes, Uri golden) async {
+    return switch (_mode) {
+      _CannedComparisonMode.alwaysPass => true,
+      _CannedComparisonMode.alwaysFail => false,
+      _CannedComparisonMode.alwaysThrowTestFailure => throw TestFailure('An expected error'),
+      _CannedComparisonMode.alwaysThrowStateError => throw StateError('An unexpected error'),
+    };
+  }
+
+  @override
+  Uri getTestUri(Uri key, int? version) => key;
+}
+
+enum _CannedComparisonMode { alwaysPass, alwaysFail, alwaysThrowTestFailure, alwaysThrowStateError }

dev/tools/android_driver_extensions/test/skia_gold_test.dart

@@ -0,0 +1,44 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:typed_data';
+
+import 'package:android_driver_extensions/native_driver.dart';
+import 'package:android_driver_extensions/skia_gold.dart';
+import 'package:file/src/interface/file.dart';
+import 'package:flutter_goldens/skia_client.dart';
+import 'package:test/fake.dart';
+import 'package:test/test.dart';
+
+void main() {
+  // Regression test for https://github.com/flutter/flutter/issues/163051.
+  test('converts SkiaException to TestFailure in postsubmit', () async {
+    final SkiaGoldClient skiaGold = _ThrowsSkiaException();
+    await enableSkiaGoldComparatorForTesting(skiaGold, presubmit: false);
+
+    await expectLater(
+      goldenFileComparator.compare(Uint8List(0), Uri(path: 'test.png')),
+      throwsA(
+        isA<TestFailure>().having(
+          (Object e) => '$e',
+          'description',
+          contains('Skia Gold received an unapproved image in post'),
+        ),
+      ),
+    );
+  });
+}
+
+final class _ThrowsSkiaException extends Fake implements SkiaGoldClient {
+  @override
+  Future<void> auth() async {}
+
+  @override
+  Future<void> imgtestInit() async {}
+
+  @override
+  Future<bool> imgtestAdd(String testName, File goldenFile) async {
+    throw const SkiaException('Skia Gold received an unapproved image in post');
+  }
+}