From 00613bed06af890b9f09befc71de3f2aedabbacb Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Mon, 11 Jun 2018 13:10:03 +0200
Subject: [PATCH] Improved regression test for #4906.

Removing the fix about 50% of the times the test will not be able to
pass cleanly. It's very hard to write a test that will always fail, or
actually, it is possible but then it's likely that it will consistently
pass if we change some random bit, so better to use randomization here.
---
 tests/unit/scan.tcl | 68 +++++++++++++++++++++++++--------------------
 1 file changed, 38 insertions(+), 30 deletions(-)

diff --git a/tests/unit/scan.tcl b/tests/unit/scan.tcl
index a02f3a58..a8cc8116 100644
--- a/tests/unit/scan.tcl
+++ b/tests/unit/scan.tcl
@@ -238,39 +238,47 @@ start_server {tags {"scan"}} {
     }
 
     test "SCAN regression test for issue #4906" {
-        r del set
-        set toremove {}
-        array set found {}
-        for {set j 0} {$j < 500} {incr j} {
-            r sadd set $j
-            if {$j >= 100} {
-                lappend toremove $j
-            }
-        }
+        for {set k 0} {$k < 100} {incr k} {
+            r del set
+            r sadd set x; # Make sure it's not intset encoded
+            set toremove {}
+            unset -nocomplain found
+            array set found {}
 
-        # Start scanning
-        set cursor 0
-        set iteration 0
-        while {!($cursor == 0 && $iteration != 0)} {
-            lassign [r sscan set $cursor] cursor items
-
-            # Mark found items. We expect to find from 0 to 99 at the end
-            # since those elements will never be removed during the scanning.
-            foreach i $items {
-                set found($i) 1
+            # Populate the set
+            set numele [expr {100+[randomInt 1000]}]
+            for {set j 0} {$j < $numele} {incr j} {
+                r sadd set $j
+                if {$j >= 100} {
+                    lappend toremove $j
+                }
             }
-            incr iteration
-            # At some point remove most of the items to trigger the
-            # rehashing to a smaller hash table.
-            if {$iteration == 1} {
-                r srem set {*}$toremove
-            }
-        }
 
-        # Verify that SSCAN reported everything from 0 to 99
-        for {set j 0} {$j < 100} {incr j} {
-            if {![info exists found($j)]} {
-                fail "SSCAN element missing $j"
+            # Start scanning
+            set cursor 0
+            set iteration 0
+            set del_iteration [randomInt 10]
+            while {!($cursor == 0 && $iteration != 0)} {
+                lassign [r sscan set $cursor] cursor items
+
+                # Mark found items. We expect to find from 0 to 99 at the end
+                # since those elements will never be removed during the scanning.
+                foreach i $items {
+                    set found($i) 1
+                }
+                incr iteration
+                # At some point remove most of the items to trigger the
+                # rehashing to a smaller hash table.
+                if {$iteration == $del_iteration} {
+                    r srem set {*}$toremove
+                }
+            }
+
+            # Verify that SSCAN reported everything from 0 to 99
+            for {set j 0} {$j < 100} {incr j} {
+                if {![info exists found($j)]} {
+                    fail "SSCAN element missing $j"
+                }
             }
         }
     }