Change LoadModelFromString to return a smart pointer, add MakeData, and update tests to have C++ RAII clean up model and data.

PiperOrigin-RevId: 935980153
Change-Id: I41d25bfab4935494dc984168820cb7cad123cadf

test/fixture.h

@@ -25,6 +25,7 @@
 #include <string>
 #include <string_view>
 #include <vector>
+#include <memory>
 
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
@@ -39,6 +40,20 @@ MJAPI mjfLogHandler _mjPRIVATE_setTlsLogHandler(mjfLogHandler handler);
 
 namespace mujoco {
 
+struct MjModelDeleter {
+  void operator()(mjModel* m) const {
+    mj_deleteModel(m);
+  }
+};
+using MjModelPtr = std::unique_ptr<mjModel, MjModelDeleter>;
+
+struct MjDataDeleter {
+  void operator()(mjData* d) const {
+    mj_deleteData(d);
+  }
+};
+using MjDataPtr = std::unique_ptr<mjData, MjDataDeleter>;
+
 // Runtime scale factor for test tolerances, controlled by MJTOL_SCALE env var.
 // Set MJTOL_SCALE=0 to run tests with zero tolerance and see actual residuals.
 inline mjtNum MjTolScale() {
@@ -189,9 +204,12 @@ const std::string GetModelPath(std::string_view path);
 
 // Returns a newly-allocated mjModel, loaded from the contents of xml.
 // On failure returns nullptr and populates the error array if present.
-mjModel* LoadModelFromString(std::string_view xml, char* error = nullptr,
+MjModelPtr LoadModelFromString(std::string_view xml, char* error = nullptr,
                              int error_size = 0, mjVFS* vfs = nullptr);
 
+// Returns a newly-allocated mjData, initialized using model.
+MjDataPtr MakeData(const MjModelPtr& model);
+
 // Returns a newly-allocated mjModel, loaded from the contents in model_path.
 // On failure it asserts that model is null.
 mjModel* LoadModelFromPath(const char* model_path);