add unit tests to permutation method

Author: EvandroLG

src/array/init.lua

@@ -577,17 +577,20 @@ array = {
     return obj[math.random(#obj)]
   end,
 
+  -- Creates a new table returning all permutations of length of the elements of the given table
+  -- @param obj {table}
+  -- @return {table}
   permutation = function(obj)
     if #obj == 1 then
       return { obj }
     end
 
     local output = {}
-    local partialList = array.permutation(array.slice(obj, 2))
+    local partial_list = array.permutation(array.slice(obj, 2))
     local first = { obj[1] }
 
-    for i=1, #partialList do
-      local partial = partialList[i]
+    for i=1, #partial_list do
+      local partial = partial_list[i]
 
       for j=1, #partial+1 do
         local merged = array.concat(

test.lua

@@ -367,3 +367,13 @@ test('random', function(a)
 
   a.equal(array.random({ 'a' }), 'a')
 end)
+
+test('permutation', function(a)
+  a.deep_equal(
+    array.permutation({ 'lua', 'javascript' }),
+    {
+      { 'lua', 'javascript' },
+      { 'javascript', 'lua' },
+    }
+  )
+end)