Actually fix C++ test

Author: scotts

test/VideoDecoderTest.cpp

@@ -50,10 +50,19 @@ class SingleStreamDecoderTest : public testing::TestWithParam<bool> {
       outputStringStream << input.rdbuf();
       content_ = outputStringStream.str();
 
-      void* buffer = content_.data();
-      size_t length = content_.length();
-      auto contextHolder =
-          std::make_unique<AVIOFromTensorContext>(buffer, length);
+      // Note that we copy the data from the string into a new buffer. The
+      // tensor has ownership of that buffer. This is not strictly necessary,
+      // as the lifetime of the content_ string will outlast the decoder. But,
+      // we do it to test the common usage where the decoder should own the
+      // memory through the tensor.
+      int64_t length = content_.length();
+      char* data = new char[length];
+      std::memcpy(data, content_.data(), length);
+      auto deleter = [data](void*) { delete[] data; };
+      at::Tensor tensor = at::from_blob(
+          static_cast<void*>(data), {length}, deleter, {torch::kUInt8});
+
+      auto contextHolder = std::make_unique<AVIOFromTensorContext>(tensor);
       return std::make_unique<SingleStreamDecoder>(
           std::move(contextHolder), SingleStreamDecoder::SeekMode::approximate);
     } else {