libtorch-bin: cleanup passthru test

- Make passthru.tests an attrset.
- Remove CMake VERBOSE option.
- Remove spurious `cat CMakeLists.txt`.
- Run the test as well.
- Actually test some functionality.

pkgs/development/libraries/science/math/libtorch/bin.nix

···
 
   outputs = [ "out" "dev" ];
 
-  passthru.tests = callPackage ./test { };
+  passthru.tests.cmake = callPackage ./test { };
 
   meta = with stdenv.lib; {
     description = "C++ API of the PyTorch machine learning framework";

pkgs/development/libraries/science/math/libtorch/test/default.nix

···
 
   src = ./.;
 
-  postPatch = ''
-    cat CMakeLists.txt
-  '';
-
-  makeFlags = [ "VERBOSE=1" ];
-
   nativeBuildInputs = [ cmake ];
 
   buildInputs = [ libtorch-bin ];
+
+  doCheck = true;
 
   installPhase = ''
     touch $out

pkgs/development/libraries/science/math/libtorch/test/test.cpp

···
+#undef NDEBUG
+#include <cassert>
+
+#include <iostream>
+
 #include <torch/torch.h>
-#include <iostream>
 
 int main() {
   torch::Tensor tensor = torch::eye(3);
-  std::cout << tensor << std::endl;
+
+  float checkData[] = {
+    1, 0, 0,
+    0, 1, 0,
+    0, 0, 1
+  };
+
+  torch::Tensor check = torch::from_blob(checkData, {3, 3});
+
+  assert(tensor.allclose(check));
 }