tests/heapalloc_exc_raise.py: Heap alloc test for raising/catching exc.

tests/micropython/heapalloc_exc_raise.py

+# Test that we can raise and catch (preallocated) exception
+# without memory allocation.
+import micropython
+
+e = ValueError("error")
+
+def func():
+    try:
+        # This works as is because traceback is not allocated
+        # if not possible (heap is locked, no memory). If heap
+        # is not locked, this would allocate a traceback entry.
+        # To avoid that, traceback should be warmed up (by raising
+        # it once after creation) and then cleared before each
+        # raise with:
+        # e.__traceback__ = None
+        raise e
+    except Exception as e2:
+        print(e2)
+
+micropython.heap_lock()
+func()
+print("ok")
+micropython.heap_unlock()

tests/micropython/heapalloc_exc_raise.py.exp

+error
+ok