Add C++ interface for the Python interpreter

tests/test_embed/catch.cpp

@@ -1,5 +1,16 @@
-// Catch provides the `int main()` function here. This is a standalone
+// The Catch implementation is compiled here. This is a standalone
 // translation unit to avoid recompiling it for every test change.
 
-#define CATCH_CONFIG_MAIN
+#include <pybind11/embed.h>
+
+#define CATCH_CONFIG_RUNNER
 #include <catch.hpp>
+
+namespace py = pybind11;
+
+int main(int argc, const char *argv[]) {
+    py::scoped_interpreter guard{};
+    auto result = Catch::Session().run(argc, argv);
+
+    return result < 0xff ? result : 0xff;
+}