Issue #330 regression test.

tests/unit/type/hash.tcl

@@ -318,6 +318,14 @@ start_server {tags {"hash"}} {
         lappend rv [string match "ERR*not an integer*" $bigerr]
     } {1 1}
 
+    test {HINCRBY can detect overflows} {
+        set e {}
+        r hset hash n -9223372036854775484
+        assert {[r hincrby hash n -1] == -9223372036854775485}
+        catch {r hincrby hash n -10000} e
+        set e
+    } {*overflow*}
+
     test {HINCRBYFLOAT against non existing database key} {
         r del htest
         list [r hincrbyfloat htest foo 2.5]