skip 5.2 tests on 5.1 mode

spec/metamethods_spec.lua

@@ -1,6 +1,10 @@
 local class = require 'middleclass'
 local Object = class.Object
 
+local function is_lua_5_2_compatible()
+  return type(rawlen) == 'function'
+end
+
 describe('Metamethods', function()
 
   describe('Custom Metamethods', function()
@@ -56,28 +60,45 @@ describe('Metamethods', function()
       __concat =   { a..b, 28 },
       __call =     { a(), math.sqrt(14) },
       __pow =      { a^b,  Vector(0,0,0) },
-      __mul =      { 4*a,  Vector(4,8,12) },
+      __mul =      { 4*a,  Vector(4,8,12) }
-      __len =      { #a,  3},
       --__index =    { b[1], 3 }
     }) do
-      it(metamethod .. ' works as expected', function()
+      describe(metamethod, function()
+        it('works as expected', function()
           assert.equal(values[1], values[2])
         end)
+      end)
     end
-    it('__pairs works as expected',function() 
+
+    if is_lua_5_2_compatible() then
+
+      describe('__len', function()
+        it('works as expected', function()
+          assert.equal(#a, 3)
+        end)
+      end)
+
+      describe('__pairs', function()
+        it('works as expected',function()
           local output = {}
           for k,v in pairs(a) do
             output[k] = v
           end
           assert.are.same(output,{x=1,y=2,z=3})
         end)
-    it('__ipairs works as expected',function() 
+      end)
+
+      describe('__ipairs', function()
+        it('works as expected',function()
           local output = {}
           for _,i in ipairs(a) do
             output[#output+1] = i
           end
           assert.are.same(output,{1,2,3})
         end)
+      end)
+
+    end
 
     describe('Inherited Metamethods', function()
       local Vector2= class('Vector2', Vector)
@@ -98,26 +119,43 @@ describe('Metamethods', function()
         __call =     { c(), math.sqrt(14) },
         __pow =      { c^d,  Vector(0,0,0) },
         __mul =      { 4*c,  Vector(4,8,12) },
-        __len =      { #c,  3},
       }) do
-        it(metamethod .. ' works as expected', function()
+        describe(metamethod, function()
+          it('works as expected', function()
             assert.equal(values[1], values[2])
           end)
+        end)
       end
-      it('__pairs works as expected',function() 
+
+      if is_lua_5_2_compatible() then
+
+        describe('__len', function()
+          it('works as expected', function()
+            assert.equal(#c, 3)
+          end)
+        end)
+
+        describe('__pairs', function()
+          it('works as expected',function()
             local output = {}
             for k,v in pairs(c) do
               output[k] = v
             end
             assert.are.same(output,{x=1,y=2,z=3})
           end)
-      it('__ipairs works as expected',function() 
+        end)
+
+        describe('__ipairs', function()
+          it('works as expected', function()
             local output = {}
             for _,i in ipairs(c) do
               output[#output+1] = i
             end
             assert.are.same(output,{1,2,3})
           end)
+        end)
+
+      end
 
     end)