Improved the [role] unit test

A new unit test, called 'test_role_lua' was added, to ensure that the [role]
tag could be used from Lua.
Also, in the first unit test the types list is stored in a variable, to
ensure that variable substitution works as intended

data/test/scenarios/test_role_types.cfg

@@ -12,10 +12,15 @@
     [event]
         name=start
 
+        [set_variable]
+            name=roles
+            value=Spectre,Nightgaunt,Wraith,Shadow,Ghost
+        [/set_variable]
+
         [role]
             role=advisor
             side=1
-            type=Spectre,Nightgaunt,Wraith,Shadow,Ghost
+            type=$roles
         [/role]
 
         [recall]
@@ -90,3 +95,38 @@
         {RETURN ([true][/true])}
     [/event]
 )}
+
+{GENERIC_UNIT_TEST "test_role_lua" (
+    [event]
+        name=start
+
+        {UNIT 1 "Dwarvish Thunderguard" recall recall (id=wrong_0)}
+        {UNIT 1 "Dwarvish Steelclad" recall recall (id=correct)}
+        {UNIT 1 "Dwarvish Fighter" recall recall (id=wrong_1)}
+        {UNIT 1 "Dwarvish Thunderer" recall recall (id=wrong_2)}
+
+        [lua]
+            code=<<
+                local types = "Dwarvish Steelclad,Dwarvish Thunderguard,Dwarvish Fighter,Dwarvish Thunderer"
+
+                wesnoth.wml_actions.role { type = types, role = "scout" }
+            >>
+        [/lua]
+
+        [recall]
+            role=scout
+        [/recall]
+
+        {ASSERT (
+            [have_unit]
+                role=scout
+                side=1
+                type=Dwarvish Steelclad
+                id=correct
+                search_recall_list=no
+            [/have_unit]
+        )}
+
+        {RETURN ([true][/true])}
+    [/event]
+)}

wml_test_schedule

@@ -90,6 +90,7 @@
 0 test_role_1
 0 test_role_2
 0 test_role_3
+0 test_role_lua
 #
 # LUA
 #