<< ", n = " << n;
        }
        // Verify the contents of the read.
        std::vector<char>::const_iterator begin = buf.begin() + offset;
        std::vector<char>::const_iterator end =
            offset + n > buf.size() ? buf.end() : begin + n;
        std::vector<char> want(begin, end);
        EXPECT_EQ(got, want) << "block size = " << block_size