Generalize LRU Cache to any objects.

pkg/front_end/test/src/byte_store/cache_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:front_end/src/byte_store/cache.dart';
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(CacheTest);
+  });
+}
+
+List<int> _b(int length) {
+  return new List<int>(length);
+}
+
+@reflectiveTest
+class CacheTest {
+  test_get_notFound_evict() {
+    var cache = _newBytesCache(100);
+
+    // Request '1'.  Nothing found.
+    expect(cache.get('1', _noBytes), isNull);
+
+    // Add enough data to the store to force an eviction.
+    cache.put('2', _b(40));
+    cache.put('3', _b(40));
+    cache.put('4', _b(40));
+  }
+
+  test_get_notFound_retry() {
+    var cache = _newBytesCache(100);
+
+    // Request '1'.  Nothing found.
+    expect(cache.get('1', _noBytes), isNull);
+
+    // Request '1' again.
+    // The previous `null` result should not have been cached.
+    expect(cache.get('1', () => _b(40)), isNotNull);
+  }
+
+  test_get_put_evict() {
+    var cache = _newBytesCache(100);
+
+    // Keys: [1, 2].
+    cache.put('1', _b(40));
+    cache.put('2', _b(50));
+
+    // Request '1', so now it is the most recently used.
+    // Keys: [2, 1].
+    cache.get('1', _noBytes);
+
+    // 40 + 50 + 30 > 100
+    // So, '2' is evicted.
+    cache.put('3', _b(30));
+    expect(cache.get('1', _noBytes), hasLength(40));
+    expect(cache.get('2', _noBytes), isNull);
+    expect(cache.get('3', _noBytes), hasLength(30));
+  }
+
+  test_put_evict_first() {
+    var cache = _newBytesCache(100);
+
+    // 40 + 50 < 100
+    cache.put('1', _b(40));
+    cache.put('2', _b(50));
+    expect(cache.get('1', _noBytes), hasLength(40));
+    expect(cache.get('2', _noBytes), hasLength(50));
+
+    // 40 + 50 + 30 > 100
+    // So, '1' is evicted.
+    cache.put('3', _b(30));
+    expect(cache.get('1', _noBytes), isNull);
+    expect(cache.get('2', _noBytes), hasLength(50));
+    expect(cache.get('3', _noBytes), hasLength(30));
+  }
+
+  test_put_evict_firstAndSecond() {
+    var cache = _newBytesCache(100);
+
+    // 10 + 80 < 100
+    cache.put('1', _b(10));
+    cache.put('2', _b(80));
+    expect(cache.get('1', _noBytes), hasLength(10));
+    expect(cache.get('2', _noBytes), hasLength(80));
+
+    // 10 + 80 + 30 > 100
+    // So, '1' and '2' are evicted.
+    cache.put('3', _b(30));
+    expect(cache.get('1', _noBytes), isNull);
+    expect(cache.get('2', _noBytes), isNull);
+    expect(cache.get('3', _noBytes), hasLength(30));
+  }
+
+  Cache<String, List<int>> _newBytesCache(int maxSizeBytes) =>
+      new Cache<String, List<int>>(maxSizeBytes, (bytes) => bytes.length);
+
+  static List<int> _noBytes() => null;
+}