Adding code. Closes #0.

test/filesystem_for_testing.h

@@ -0,0 +1,61 @@
+// Copyright 2017 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Implements a fake filesystem, useful for tests.
+#ifndef THIRD_PARTY_CPU_FEATURES_TEST_FILESYSTEM_FOR_TESTING_H_
+#define THIRD_PARTY_CPU_FEATURES_TEST_FILESYSTEM_FOR_TESTING_H_
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+#include "internal/filesystem.h"
+
+namespace cpu_features {
+
+class FakeFile {
+ public:
+  explicit FakeFile(int file_descriptor, const char* content);
+  ~FakeFile();
+
+  void Open();
+  void Close();
+  int Read(int fd, void* buf, size_t count);
+
+  int GetFileDescriptor() const { return file_descriptor_; }
+
+ private:
+  const int file_descriptor_;
+  const std::string content_;
+  bool opened_ = false;
+  size_t head_index_ = 0;
+};
+
+class FakeFilesystem {
+ public:
+  void Reset();
+  FakeFile* CreateFile(const std::string& filename, const char* content);
+  FakeFile* FindFileOrDie(const int file_descriptor) const;
+  FakeFile* FindFileOrNull(const std::string& filename) const;
+
+ private:
+  size_t next_file_descriptor_ = 0;
+  std::unordered_map<std::string, std::unique_ptr<FakeFile>> files_;
+};
+
+FakeFilesystem& GetEmptyFilesystem();
+
+}  // namespace cpu_features
+
+#endif  // THIRD_PARTY_CPU_FEATURES_TEST_FILESYSTEM_FOR_TESTING_H_