add BuildStepImpl tests

lib/build.dart

@@ -2,9 +2,13 @@
 // 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.
 export 'src/asset/asset.dart';
+export 'src/asset/exceptions.dart';
 export 'src/asset/id.dart';
+export 'src/asset/reader.dart';
+export 'src/asset/writer.dart';
 export 'src/builder/build_step.dart';
 export 'src/builder/builder.dart';
+export 'src/builder/exceptions.dart';
 export 'src/generate/build_result.dart';
 export 'src/generate/build.dart';
 export 'src/generate/input_set.dart';

lib/src/asset/exceptions.dart

@@ -0,0 +1,13 @@
+// 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 'id.dart';
+
+class AssetNotFoundException implements Exception {
+  final AssetId assetId;
+
+  AssetNotFoundException(this.assetId);
+
+  @override
+  String toString() => 'AssetNotFoundException: $assetId';
+}

lib/src/builder/build_step_impl.dart

@@ -10,6 +10,7 @@ import '../asset/id.dart';
 import '../asset/reader.dart';
 import '../asset/writer.dart';
 import 'build_step.dart';
+import 'exceptions.dart';
 
 /// A single step in the build processes. This represents a single input and
 /// its expected and real outputs. It also handles tracking of dependencies.
@@ -61,8 +62,14 @@ class BuildStepImpl implements BuildStep {
 
   /// Outputs an [Asset] using the current [AssetWriter], and adds [asset] to
   /// [outputs].
+  ///
+  /// Throws an [UnexpectedOutputException] if [asset] is not in
+  /// [expectedOutputs].
   @override
   void writeAsString(Asset asset, {Encoding encoding: UTF8}) {
+    if (!expectedOutputs.any((id) => id == asset.id)) {
+      throw new UnexpectedOutputException(asset);
+    }
     _outputs.add(asset);
     var done = _writer.writeAsString(asset, encoding: encoding);
     _outputsCompleted = _outputsCompleted.then((_) => done);

lib/src/builder/exceptions.dart

@@ -0,0 +1,13 @@
+// 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 '../asset/asset.dart';
+
+class UnexpectedOutputException implements Exception {
+  final Asset asset;
+
+  UnexpectedOutputException(this.asset);
+
+  @override
+  String toString() => 'UnexpectedOutputException: $asset';
+}

test/builder/build_step_impl_test.dart

@@ -0,0 +1,111 @@
+// 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.
+@TestOn('vm')
+import 'package:test/test.dart';
+
+import 'package:build/build.dart';
+import 'package:build/src/builder/build_step_impl.dart';
+
+import '../common/common.dart';
+
+main() {
+  group('BuildStepImpl ', () {
+    AssetWriter writer;
+    AssetReader reader;
+
+    group('with reader/writer stub', () {
+      Asset primary;
+      BuildStepImpl buildStep;
+
+      setUp(() {
+        reader = new StubAssetReader();
+        writer = new StubAssetWriter();
+        primary = makeAsset();
+        buildStep = new BuildStepImpl(primary, [], reader, writer);
+      });
+
+      test('tracks dependencies on read', () async {
+        expect(buildStep.dependencies, [primary.id]);
+
+        var a1 = makeAssetId();
+        await buildStep.readAsString(a1);
+        expect(buildStep.dependencies, [primary.id, a1]);
+
+        var a2 = makeAssetId();
+        await buildStep.readAsString(a2);
+        expect(buildStep.dependencies, [primary.id, a1, a2]);
+      });
+
+      test('addDependency adds dependencies', () {
+        expect(buildStep.dependencies, [primary.id]);
+
+        var a1 = makeAssetId();
+        buildStep.addDependency(a1);
+        expect(buildStep.dependencies, [primary.id, a1]);
+
+        var a2 = makeAssetId();
+        buildStep.addDependency(a2);
+        expect(buildStep.dependencies, [primary.id, a1, a2]);
+      });
+
+      test('tracks outputs', () async {
+        var a1 = makeAsset();
+        var a2 = makeAsset();
+        buildStep = new BuildStepImpl(primary, [a1.id, a2.id], reader, writer);
+
+        buildStep.writeAsString(a1);
+        expect(buildStep.outputs, [a1]);
+
+        buildStep.writeAsString(a2);
+        expect(buildStep.outputs, [a1, a2]);
+
+        expect(buildStep.outputsCompleted, completes);
+      });
+
+      test('doesnt allow non-expected outputs', () {
+        var asset = makeAsset();
+        expect(() => buildStep.writeAsString(asset),
+            throwsA(new isInstanceOf<UnexpectedOutputException>()));
+      });
+    });
+
+    group('with in memory file system', () {
+      InMemoryAssetWriter writer;
+      InMemoryAssetReader reader;
+
+      setUp(() {
+        writer = new InMemoryAssetWriter();
+        reader = new InMemoryAssetReader(writer.assets);
+      });
+
+      test('tracks dependencies and outputs when used by a builder', () async {
+        var fileCombiner = new FileCombinerBuilder();
+        var primary = 'a|web/primary.txt';
+        var unUsed = 'a|web/not_used.txt';
+        var inputs = makeAssets({
+          primary: 'a|web/a.txt\na|web/b.txt',
+          'a|web/a.txt': 'A',
+          'a|web/b.txt': 'B',
+          unUsed: 'C',
+        });
+        addAssets(inputs.values, writer);
+        var outputId = new AssetId.parse('$primary.combined');
+        var buildStep = new BuildStepImpl(
+            inputs[new AssetId.parse(primary)], [outputId], reader, writer);
+
+        await fileCombiner.build(buildStep);
+        await buildStep.outputsCompleted;
+
+        // All the assets should be read and marked as deps, except [unUsed].
+        expect(buildStep.dependencies,
+            inputs.keys.where((k) => k != new AssetId.parse(unUsed)));
+
+        // One output.
+        expect(buildStep.outputs[0].id, outputId);
+        expect(buildStep.outputs[0].stringContents, 'AB');
+        expect(writer.assets[outputId], 'AB');
+      });
+    });
+  });
+}

test/common/common.dart

@@ -1,5 +1,43 @@
 // 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:build/build.dart';
+
+import 'in_memory_writer.dart';
+
 export 'copy_builder.dart';
+export 'file_combiner_builder.dart';
+export 'in_memory_reader.dart';
+export 'in_memory_writer.dart';
 export 'generic_builder_transformer.dart';
+export 'stub_reader.dart';
+export 'stub_writer.dart';
+
+int _nextId = 0;
+AssetId makeAssetId([String assetIdString]) {
+  if (assetIdString == null) {
+    assetIdString = 'a|web/asset_$_nextId.txt';
+    _nextId++;
+  }
+  return new AssetId.parse(assetIdString);
+}
+
+Asset makeAsset([String assetIdString, String contents]) {
+  var id = makeAssetId(assetIdString);
+  return new Asset(id, contents ?? '$id');
+}
+
+Map<AssetId, Asset> makeAssets(Map<String, String> assetsMap) {
+  var assets = <AssetId, Asset>{};
+  assetsMap.forEach((idString, content) {
+    var asset = makeAsset(idString, content);
+    assets[asset.id] = asset;
+  });
+  return assets;
+}
+
+void addAssets(Iterable<Asset> assets, InMemoryAssetWriter writer) {
+  for (var asset in assets) {
+    writer.assets[asset.id] = asset.stringContents;
+  }
+}

test/common/file_combiner_builder.dart

@@ -0,0 +1,28 @@
+// 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 'dart:async';
+
+import 'package:build/build.dart';
+
+/// Takes an input file which points at a bunch of other files, and then it
+/// writes an `$input.combined` file which concats all the files.
+class FileCombinerBuilder implements Builder {
+  Future build(BuildStep buildStep) async {
+    var lines = buildStep.input.stringContents.split('\n');
+    var content = new StringBuffer();
+    for (var line in lines) {
+      content.write(await buildStep.readAsString(new AssetId.parse(line)));
+    }
+
+    var outputId = _combinedAssetId(buildStep.input.id);
+    buildStep.writeAsString(new Asset(outputId, content.toString()));
+  }
+
+  List<AssetId> declareOutputs(AssetId input) {
+    return [_combinedAssetId(input)];
+  }
+}
+
+AssetId _combinedAssetId(AssetId inputId) =>
+    inputId.addExtension('.combined');

test/common/in_memory_reader.dart

@@ -0,0 +1,18 @@
+// 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 'dart:async';
+import 'dart:convert';
+
+import 'package:build/build.dart';
+
+class InMemoryAssetReader implements AssetReader {
+  final Map<AssetId, String> assets;
+
+  InMemoryAssetReader(this.assets);
+
+  Future<String> readAsString(AssetId id, {Encoding encoding: UTF8}) async {
+    if (!assets.containsKey(id)) throw new AssetNotFoundException(id);
+    return assets[id];
+  }
+}

test/common/in_memory_writer.dart

@@ -0,0 +1,17 @@
+// 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 'dart:async';
+import 'dart:convert';
+
+import 'package:build/build.dart';
+
+class InMemoryAssetWriter implements AssetWriter {
+  final Map<AssetId, String> assets = {};
+
+  InMemoryAssetWriter();
+
+  Future writeAsString(Asset asset, {Encoding encoding: UTF8}) async {
+    assets[asset.id] = asset.stringContents;
+  }
+}

test/common/stub_reader.dart

@@ -0,0 +1,12 @@
+// 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 'dart:async';
+import 'dart:convert';
+
+import 'package:build/build.dart';
+
+class StubAssetReader implements AssetReader {
+  Future<String> readAsString(AssetId id, {Encoding encoding: UTF8}) =>
+      new Future.value(null);
+}

test/common/stub_writer.dart

@@ -0,0 +1,12 @@
+// 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 'dart:async';
+import 'dart:convert';
+
+import 'package:build/build.dart';
+
+class StubAssetWriter implements AssetWriter {
+  Future writeAsString(Asset asset, {Encoding encoding: UTF8}) =>
+      new Future.value(null);
+}