Test: added a memory efficiency test.

tests/test_helper.tcl

@@ -45,6 +45,7 @@ set ::all_tests {
     unit/limits
     unit/obuf-limits
     unit/bitops
+    unit/memefficiency
 }
 # Index to the next test to run in the ::all_tests list.
 set ::next_test 0

tests/unit/memefficiency.tcl

@@ -0,0 +1,32 @@
+proc test_memory_efficiency {range} {
+    r flushall
+    set base_mem [s used_memory]
+    set written 0
+    for {set j 0} {$j < 10000} {incr j} {
+        set key key:$j
+        set val [string repeat A [expr {int(rand()*$range)}]]
+        r set $key $val
+        incr written [string length $key]
+        incr written [string length $val]
+        incr written 2 ;# A separator is the minimum to store key-value data.
+    }
+    set current_mem [s used_memory]
+    set used [expr {$current_mem-$base_mem}]
+    set efficiency [expr {double($written)/$used}]
+    return $efficiency
+}
+
+start_server {tags {"memefficiency"}} {
+    foreach {size_range expected_min_efficiency} {
+        32    0.15
+        64    0.25
+        128   0.35
+        1024  0.75
+        16384 0.90
+    } {
+        test "Memory efficiency with values in range $size_range" {
+            set efficiency [test_memory_efficiency $size_range]
+            assert {$efficiency >= $expected_min_efficiency}
+        }
+    }
+}