fixes #4818

tests/system/tdeepcopy.nim

@@ -1,6 +1,5 @@
 discard """
   output: "ok"
-  disabled: "true"
 """
 
 import tables, lists

tests/system/trealloc.nim

@@ -0,0 +1,21 @@
+discard """
+  output: '''success'''
+"""
+
+# bug #4818
+
+# Test that this completes without OOM.
+
+const BUFFER_SIZE = 5000
+var buffer = cast[ptr uint16](alloc(BUFFER_SIZE))
+
+var total_size: int64 = 0
+for i in 0 .. 4000:
+    let size = BUFFER_SIZE * i
+    #echo "requesting ", size
+    total_size += size.int64
+    buffer = cast[ptr uint16](realloc(buffer, size))
+    #echo totalSize, " total: ", getTotalMem(), " occupied: ", getOccupiedMem(), " free: ", getFreeMem()
+
+dealloc(buffer)
+echo "success"