std::unique_ptr<ReadOnlyMemoryRegion> region;
  Status status = env_->NewReadOnlyMemoryRegionFromFile(filepath, &region);
  EXPECT_PRED2(UnimplementedOrReturnsCode, status, Code::NOT_FOUND);
}

TEST_P(ModularFileSystemTest, TestCreateMemoryRegionNonExisting) {
  const std::string filepath = GetURIForPath("dir_not_found/a_file");
  std::unique_ptr<ReadOnlyMemoryRegion> region;

/// operation pointers may change.
///
/// There are 4 function tables: one for each of the 3 file objects in
/// TensorFlow (i.e., `RandomAccessFile`, `WritableFile`,
/// `ReadOnlyMemoryRegion`) and one for all the operations a `Filesystem`
/// implements. Each of them is in a 1-to-1 correspondence with the wrapper
/// structures from the first section: these tables only contain function