The following modifications solved the problem:

static PyMethodDef pyModuleMethods[] = {
    { "runTester", (PyCFunction)runTesterFunc, METH_VARARGS | METH_KEYWORDS, "Foo Boo." },
    { NULL, NULL, 0, NULL }
};

static struct PyModuleDef MyModule = {
    PyModuleDef_HEAD_INIT,
    "my_module",
    "Foo Boo.",
    -1,
    pyModuleMethods,
    NULL
};