Issue #10914: Add a minimal embedding test to test_capi.

Modules/_testembed.c

@@ -0,0 +1,52 @@
+#include <Python.h>
+#include <stdio.h>
+
+void print_subinterp(void)
+{
+    /* Just output some debug stuff */
+    PyThreadState *ts = PyThreadState_Get();
+    printf("interp %p, thread state %p: ", ts->interp, ts);
+    fflush(stdout);
+    PyRun_SimpleString(
+        "import sys;"
+        "print('id(modules) =', id(sys.modules));"
+        "sys.stdout.flush()"
+    );
+}
+
+int main(int argc, char *argv[])
+{
+    PyThreadState *mainstate, *substate;
+    PyGILState_STATE gilstate;
+    int i, j;
+
+    for (i=0; i<3; i++) {
+        printf("--- Pass %d ---\n", i);
+        /* HACK: the "./" at front avoids a search along the PATH in
+           Modules/getpath.c */
+        Py_SetProgramName(L"./_testembed");
+        Py_Initialize();
+        mainstate = PyThreadState_Get();
+
+        PyEval_InitThreads();
+        PyEval_ReleaseThread(mainstate);
+
+        gilstate = PyGILState_Ensure();
+        print_subinterp();
+        PyThreadState_Swap(NULL);
+
+        for (j=0; j<3; j++) {
+            substate = Py_NewInterpreter();
+            print_subinterp();
+            Py_EndInterpreter(substate);
+        }
+
+        PyThreadState_Swap(mainstate);
+        print_subinterp();
+        PyGILState_Release(gilstate);
+
+        PyEval_RestoreThread(mainstate);
+        Py_Finalize();
+    }
+    return 0;
+}