tests: Move heap-realloc-while-locked test from C to Python.

This test for calling gc_realloc() while the GC is locked can be done in
pure Python, so better to do it that way since it can then be tested on
more ports.

ports/unix/coverage.c

@@ -169,14 +169,8 @@ STATIC mp_obj_t extra_coverage(void) {
         gc_free(NULL);
         gc_unlock();
 
-        // calling gc_realloc while GC is locked
-        void *p = gc_alloc(4, false);
-        gc_lock();
-        mp_printf(&mp_plat_print, "%p\n", gc_realloc(p, 8, true));
-        gc_unlock();
-
         // using gc_realloc to resize to 0, which means free the memory
-        p = gc_alloc(4, false);
+        void *p = gc_alloc(4, false);
         mp_printf(&mp_plat_print, "%p\n", gc_realloc(p, 0, false));
 
         // calling gc_nbytes with a non-heap pointer

tests/micropython/heap_lock.py

@@ -2,13 +2,24 @@
 
 import micropython
 
+l = []
+l2 = list(range(100))
+
 micropython.heap_lock()
 
+# general allocation on the heap
 try:
     print([])
 except MemoryError:
     print('MemoryError')
 
+# expansion of a heap block
+try:
+    l.extend(l2)
+except MemoryError:
+    print('MemoryError')
+
 micropython.heap_unlock()
 
+# check that allocation works after an unlock
 print([])

tests/micropython/heap_lock.py.exp

@@ -1,2 +1,3 @@
 MemoryError
+MemoryError
 []

tests/unix/extra_coverage.py.exp

@@ -16,7 +16,6 @@ abc
 # GC
 0
 0
-0
 # vstr
 tests
 sts