add unit test for an object-based "feeding" ability

based on tekelili's forum post here:
http://forums.wesnoth.org/viewtopic.php?f=8&t=40449#p572206

data/test/scenarios/feeding.cfg

@@ -0,0 +1,162 @@
+# This unit test defines a WML object based implementation of the "feeding" ability
+# and checks that it works. What is being tested here, beyond what is tested in
+# test_unit_map and other scenarios that test the attack pathway, is that 
+# - the die event works
+# - objects attach to units by id correctly
+# - abilities can be properly detected in filters
+# - abillities which add other objects works
+# - this impl of feeding works
+
+#define STR_FEEDING 
+foo
+#enddef
+
+#define STR_FEEDING_EFFECT 
+bar
+#enddef
+
+#define STR_FEEDING_DESCRIPTION
+baz
+#enddef
+
+#define TEST_FEEDING ID EXPECTED_INCREASE
+    [store_unit]
+        [filter]
+            id={ID}
+        [/filter]
+        variable=Killer
+    [/store_unit]
+
+    {VARIABLE victim_x $Killer.x}
+    {VARIABLE_OP victim_x sub 1}
+    {VARIABLE victim_y $Killer.y}
+
+    {VARIABLE victim_side 3}
+    {VARIABLE_OP victim_side sub $Killer.side|}
+
+    {VARIABLE Killer_start_hp $Killer.hitpoints}
+
+    [terrain_mask]
+        x,y=$victim_x|,$victim_y|
+        mask="Xv"
+    [/terrain_mask]
+    {UNIT $victim_side| "Elvish Archer" $victim_x| $victim_y| (hitpoints=1)}
+    [do_command]
+        [attack]
+            weapon = 0
+            defender_weapon = 0
+            [source]
+                x,y=$Killer.x|,$Killer.y|
+            [/source]
+            [destination]
+                x,y=$victim_x|,$victim_y|
+            [/destination]
+        [/attack]
+    [/do_command]
+
+    [store_unit]
+        [filter]
+            id={ID}
+        [/filter]
+        variable=Killer
+    [/store_unit]
+
+    {VARIABLE_OP Killer_start_hp add {EXPECTED_INCREASE}}
+
+    {ASSERT ({VARIABLE_CONDITIONAL Killer.hitpoints equals $Killer_start_hp})}
+#enddef
+
+{GENERIC_UNIT_TEST "feeding" (
+[event]
+    id=ability_feeding_die
+    name=die
+    first_time_only=no
+    [filter]
+        [not]
+            [filter_wml]
+                [status]
+                    not_living="yes"
+                [/status]
+            [/filter_wml]
+        [/not]
+    [/filter]
+    [filter_second]
+        ability=feeding
+    [/filter_second]
+    [unstore_unit]
+        variable=second_unit
+        {COLOR_HEAL}
+        text= {STR_FEEDING_EFFECT}
+        find_vacant=no
+    [/unstore_unit]
+    [object]
+        silent=yes
+        duration=forever
+        [filter]
+            x,y=$x2|,$y2|
+        [/filter]
+        [effect]
+            apply_to=hitpoints
+            increase_total=1
+            increase=1
+        [/effect]
+    [/object]
+[/event]
+[event]
+    name=start
+    [object]
+        id=feeding_object
+        silent=yes
+        [effect]
+            apply_to=new_ability
+            [abilities]
+                [dummy]
+                    id=feeding
+                    name= {STR_FEEDING}
+                    female_name= {STR_FEEDING}
+                    description= {STR_FEEDING_DESCRIPTION}
+                [/dummy]
+            [/abilities]
+        [/effect]
+        [filter]
+            id=bob
+        [/filter]
+    [/object]
+[/event]
+[event]
+    name=start
+
+    {TEST_FEEDING alice 0}
+    {TEST_FEEDING alice 0}
+    {TEST_FEEDING alice 0}
+
+    [end_turn]
+    [/end_turn]
+[/event]
+[event]
+    name = side 2 turn 1
+
+    {TEST_FEEDING bob 1}
+    {TEST_FEEDING bob 1}
+    {TEST_FEEDING bob 1}
+
+    [store_unit]
+        [filter]
+            id=bob
+        [/filter]
+        variable=Bob
+    [/store_unit]
+
+    {VARIABLE_OP Bob.experience add 50}        
+
+    [unstore_unit]
+        variable=Bob
+    [/unstore_unit]
+
+    {TEST_FEEDING bob 1}
+    {TEST_FEEDING bob 1}
+    {TEST_FEEDING bob 1}
+
+    {RETURN ([true][/true])}
+[/event]
+)}

wml_test_schedule

@@ -102,6 +102,7 @@
 0 alice_kills_bob_on_retal_levelup
 0 test_grunt_tod_damage
 0 test_berzerk_firststrike
+0 feeding
 #
 # Deterministic unit facing tests
 0 recruit_facing_enemy_one