diff --git a/quic/test_tools/quic_stream_sequencer_buffer_peer.h b/quic/test_tools/quic_stream_sequencer_buffer_peer.h
new file mode 100644
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+++ b/quic/test_tools/quic_stream_sequencer_buffer_peer.h
@@ -0,0 +1,63 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef QUICHE_QUIC_TEST_TOOLS_QUIC_STREAM_SEQUENCER_BUFFER_PEER_H_
+#define QUICHE_QUIC_TEST_TOOLS_QUIC_STREAM_SEQUENCER_BUFFER_PEER_H_
+
+#include "net/third_party/quiche/src/quic/core/quic_stream_sequencer_buffer.h"
+
+namespace quic {
+
+namespace test {
+
+class QuicStreamSequencerBufferPeer {
+ public:
+  explicit QuicStreamSequencerBufferPeer(QuicStreamSequencerBuffer* buffer);
+  QuicStreamSequencerBufferPeer(const QuicStreamSequencerBufferPeer&) = delete;
+  QuicStreamSequencerBufferPeer& operator=(
+      const QuicStreamSequencerBufferPeer&) = delete;
+
+  // Read from this buffer_ into the given destination buffer_ up to the
+  // size of the destination. Returns the number of bytes read. Reading from
+  // an empty buffer_->returns 0.
+  size_t Read(char* dest_buffer, size_t size);
+
+  // If buffer is empty, the blocks_ array must be empty, which means all
+  // blocks are deallocated.
+  bool CheckEmptyInvariants();
+
+  bool IsBlockArrayEmpty();
+
+  bool CheckInitialState();
+
+  bool CheckBufferInvariants();
+
+  size_t GetInBlockOffset(QuicStreamOffset offset);
+
+  QuicStreamSequencerBuffer::BufferBlock* GetBlock(size_t index);
+
+  int IntervalSize();
+
+  size_t max_buffer_capacity();
+
+  size_t ReadableBytes();
+
+  void set_total_bytes_read(QuicStreamOffset total_bytes_read);
+
+  void AddBytesReceived(QuicStreamOffset offset, QuicByteCount length);
+
+  bool IsBufferAllocated();
+
+  size_t block_count();
+
+  const QuicIntervalSet<QuicStreamOffset>& bytes_received();
+
+ private:
+  QuicStreamSequencerBuffer* buffer_;
+};
+
+}  // namespace test
+}  // namespace quic
+
+#endif  // QUICHE_QUIC_TEST_TOOLS_QUIC_STREAM_SEQUENCER_BUFFER_PEER_H_