Add tests for fixed crashes

Provoked with e.g.,
    def f(a, b):
        print(a, b)

    f(1, **{len:2})

py/bc.c

@@ -190,6 +190,9 @@ void mp_setup_code_state(mp_code_state_t *code_state, size_t n_args, size_t n_kw
         for (size_t i = 0; i < n_kw; i++) {
             // the keys in kwargs are expected to be qstr objects
             mp_obj_t wanted_arg_name = kwargs[2 * i];
+            if(MP_UNLIKELY(!MP_OBJ_IS_QSTR(wanted_arg_name))) {
+                mp_raise_TypeError("unexpected keyword argument");
+            }
             for (size_t j = 0; j < n_pos_args + n_kwonly_args; j++) {
                 if (wanted_arg_name == arg_names[j]) {
                     if (code_state->state[n_state - 1 - j] != MP_OBJ_NULL) {

py/map.c

@@ -137,7 +137,10 @@ STATIC void mp_map_rehash(mp_map_t *map) {
 //  - returns NULL if not found, else the slot if was found in with key null and value non-null
 mp_map_elem_t *mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t lookup_kind) {
     // If the map is a fixed array then we must only be called for a lookup
-    assert(!map->is_fixed || lookup_kind == MP_MAP_LOOKUP);
+    if (MP_UNLIKELY(map->is_fixed && lookup_kind != MP_MAP_LOOKUP)) {
+        mp_raise_TypeError("unsupported operation on fixed map");
+    }
+
 
     // Work out if we can compare just pointers
     bool compare_only_ptrs = map->all_keys_are_qstrs;

tests/misc/crashes.py

@@ -0,0 +1,30 @@
+def assertRaises(arg):
+    if issubclass(arg, Exception):
+        def inner(fn):
+            try:
+                fn()
+            except arg:
+                print(True)
+            else: print(False)
+        return inner
+    else:
+        try:
+            fn()
+        except:
+            print(True)
+        else:
+            print(False)
+
+@assertRaises(TypeError)
+def f():
+    del str.partition
+
+@assertRaises(TypeError)
+def f():
+    property.start = 0
+
+@assertRaises(TypeError)
+def f():
+    def inner(a, b):
+        print(a, b)
+    inner(1, **{len: 2})