Override GoldenComperator with tolerance to fix problem on CI.

test/flutter_test_config.dart

@@ -1,11 +1,16 @@
 import 'dart:async';
 
+import 'package:flutter_test/flutter_test.dart';
 import 'package:golden_toolkit/golden_toolkit.dart';
 
+import 'golden_diff_comparator.dart';
 import 'test_app.dart';
 
-Future<void> testExecutable(FutureOr<void> Function() testMain) async =>
-    GoldenToolkit.runWithConfiguration(
-      () => TestApp.setupAll().then((value) => testMain()),
-      config: GoldenToolkitConfiguration(skipGoldenAssertion: () => false),
-    );
+Future<void> testExecutable(FutureOr<void> Function() testMain) async {
+  final testUrl = (goldenFileComparator as LocalFileComparator).basedir;
+  goldenFileComparator = GoldenDiffComparator('$testUrl/test.dart');
+  GoldenToolkit.runWithConfiguration(
+        () => TestApp.setupAll().then((value) => testMain()),
+    config: GoldenToolkitConfiguration(skipGoldenAssertion: () => false),
+  );
+}

test/golden_diff_comparator.dart

@@ -0,0 +1,30 @@
+import 'dart:developer';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+class GoldenDiffComparator extends LocalFileComparator {
+  GoldenDiffComparator(
+      String testFile, {
+        this.tolerance = 0.005,
+      }) : super(Uri.parse(testFile));
+
+  final double tolerance;
+
+  @override
+  Future<bool> compare(Uint8List imageBytes, Uri golden) async {
+    final ComparisonResult result = await GoldenFileComparator.compareLists(
+      imageBytes,
+      await getGoldenBytes(golden),
+    );
+
+    if (!result.passed && result.diffPercent > tolerance) {
+      final String error = await generateFailureOutput(result, golden, basedir);
+      throw FlutterError(error);
+    }
+    if (!result.passed) {
+      log('A tolerable difference of ${result.diffPercent * 100}% was found when comparing $golden.');
+    }
+    return result.passed || result.diffPercent <= tolerance;
+  }
+}