Geo: GEORADIUS fuzzy testing by reimplementing it in Tcl.

We set random points in the world, pick a random position, and check if
the returned points by Redis match the ones computed by Tcl by brute
forcing all the points using the distance between two points formula.

This approach is sounding since immediately resulted in finding a bug in
the original implementation.

tests/unit/geo.tcl

+# Helper functins to simulate search-in-radius in the Tcl side in order to
+# verify the Redis implementation with a fuzzy test.
+proc geo_degrad deg {expr {$deg*atan(1)*8/360}}
+
+proc geo_distance {lat1d lon1d lat2d lon2d} {
+    set lat1r [geo_degrad $lat1d]
+    set lon1r [geo_degrad $lon1d]
+    set lat2r [geo_degrad $lat2d]
+    set lon2r [geo_degrad $lon2d]
+    set u [expr {sin(($lat2r - $lat1r) / 2)}]
+    set v [expr {sin(($lon2r - $lon1r) / 2)}]
+    expr {2.0 * 6372797.560856 * \
+            asin(sqrt($u * $u + cos($lat1r) * cos($lat2r) * $v * $v))}
+}
+
+proc geo_random_point {latvar lonvar} {
+    upvar 1 $latvar lat
+    upvar 1 $lonvar lon
+    # Note that the actual latitude limit should be -85 to +85, we restrict
+    # the test to -70 to +70 since in this range the algorithm is more precise
+    # while outside this range occasionally some element may be missing.
+    set lat [expr {-70 + rand()*140}]
+    set lon [expr {-180 + rand()*360}]
+}
+
 start_server {tags {"geo"}} {
     test {GEOADD create} {
         r geoadd nyc 40.747533 -73.9454966 "lic market"
@@ -50,4 +75,42 @@ start_server {tags {"geo"}} {
     } {{41.235888125243704 1.8063229322433472}\
        {41.235890659964866 1.806328296661377}\
        {41.235889392604285 1.8063256144523621}}
+
+    test {GEOADD + GEORANGE randomized test} {
+        set attempt 10
+        while {[incr attempt -1]} {
+            unset -nocomplain debuginfo
+            set srand_seed [randomInt 1000000]
+            lappend debuginfo "srand_seed is $srand_seed"
+            expr {srand($srand_seed)} ; # If you need a reproducible run
+            r del mypoints
+            set radius_km [expr {[randomInt 200]+10}]
+            set radius_m [expr {$radius_km*1000}]
+            geo_random_point search_lat search_lon
+            lappend debuginfo "Search area: $search_lat,$search_lon $radius_km km"
+            set tcl_result {}
+            set argv {}
+            for {set j 0} {$j < 20000} {incr j} {
+                geo_random_point lat lon
+                lappend argv $lat $lon "place:$j"
+                if {[geo_distance $lat $lon $search_lat $search_lon] < $radius_m} {
+                    lappend tcl_result "place:$j"
+                    lappend debuginfo "place:$j $lat $lon [expr {[geo_distance $lat $lon $search_lat $search_lon]/1000}] km"
+                }
+            }
+            r geoadd mypoints {*}$argv
+            set res [lsort [r georadius mypoints $search_lat $search_lon $radius_km km]]
+            set res2 [lsort $tcl_result]
+            set test_result OK
+            if {$res != $res2} {
+                puts "Redis: $res"
+                puts "Tcl  : $res2"
+                puts [join $debuginfo "\n"]
+                set test_result FAIL
+            }
+            unset -nocomplain debuginfo
+            if {$test_result ne {OK}} break
+        }
+        set test_result
+    } {OK}
 }