Pass needed arguments and reorder state machine

- Arguments were misordered and `scale` is needed to compute the denominator.
 - Reorder "state machine" if-else as variant_unit_name is priority and "item" is too.
 - @andrewpbrett I need your review here ;)
 - Still need to test imperial system

spec/javascripts/unit/admin/products/services/unit_prices_spec.js.coffee

@@ -0,0 +1,116 @@
+describe "UnitPrices service", ->
+  UnitPrices = null
+  
+  beforeEach ->
+    module "admin.products"
+    module ($provide)->
+      $provide.value "availableUnits", "g,kg,T,mL,L,kL"
+      null
+    inject (_UnitPrices_) ->
+      UnitPrices = _UnitPrices_
+
+  describe "get correct unit price duo unit/value for weight", ->
+    unit_type = "weight"
+
+    it "with scale: 1", ->
+      price = 1
+      scale = 1
+      unit_value = 1
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 1000
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with scale and unit_value: 1000", ->
+      price = 1
+      scale = 1000
+      unit_value = 1000
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 1
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with scale: 1000 and unit_value: 2000", ->
+      price = 1
+      scale = 1000
+      unit_value = 2000
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 0.5
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with price: 2", ->
+      price = 2
+      scale = 1
+      unit_value = 1
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 2000
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with price: 2, scale and unit_value: 1000", ->
+      price = 2
+      scale = 1000
+      unit_value = 1000
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 2
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with price: 2, scale: 1000 and unit_value: 2000", ->
+      price = 2
+      scale = 1000
+      unit_value = 2000
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 1
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+    it "with price: 2, scale: 1000 and unit_value: 500", ->
+      price = 2
+      scale = 1000
+      unit_value = 500
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 4
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "kg"
+
+
+  describe "get correct unit price duo unit/value for volume", ->
+    unit_type = "volume"
+
+    it "with scale: 1", ->
+      price = 1
+      scale = 1
+      unit_value = 1
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 1
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "L"
+
+    it "with price: 2 and unit_value: 0.5", ->
+      price = 2
+      scale = 1
+      unit_value = 0.5
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 4
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "L"
+
+    it "with price: 2, scale: 0.001 and unit_value: 0.01", ->
+      price = 2
+      scale = 0.001
+      unit_value = 0.01 
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 200
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "L"
+
+    it "with price: 20000, scale: 1000 and unit_value: 10000", ->
+      price = 20000
+      scale = 1000
+      unit_value = 10000 
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 2
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "L"
+
+  describe "get correct unit price duo unit/value for items", ->
+    unit_type = "items"
+    scale = null
+
+    it "with price: 1 and unit_value: 1", ->
+      price = 1
+      unit_value = 1
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 1
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "item"
+
+    it "with price: 1 and unit_value: 10", ->
+      price = 1
+      unit_value = 10
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 0.1
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "item"
+
+    it "with price: 10 and unit_value: 1", ->
+      price = 10
+      unit_value = 1
+      expect(UnitPrices.price(price, scale, unit_type, unit_value)).toEqual 10
+      expect(UnitPrices.unit(scale, unit_type)).toEqual "item"