Adds 'decorator_class?' method

Indicates whether a class can be decorated or not without resorting to a
rescue in application-level code.

lib/draper/decoratable.rb

@@ -23,6 +23,10 @@ def decorator_class
       self.class.decorator_class
     end
 
+    def decorator_class?
+      self.class.decorator_class?
+    end
+
     # The list of decorators that have been applied to the object.
     #
     # @return [Array<Class>] `[]`
@@ -56,6 +60,12 @@ def decorate(options = {})
         decorator_class.decorate_collection(collection, options.reverse_merge(with: nil))
       end
 
+      def decorator_class?
+        decorator_class
+      rescue Draper::UninferrableDecoratorError
+        false
+      end
+
       # Infers the decorator class to be used by {Decoratable#decorate} (e.g.
       # `Product` maps to `ProductDecorator`).
       #

spec/draper/decoratable_spec.rb

@@ -46,6 +46,26 @@ module Draper
       end
     end
 
+    describe "#decorator_class?" do
+      it "returns true for decoratable model" do
+        expect(Product.new.decorator_class?).to be_true
+      end
+
+      it "returns false for non-decoratable model" do
+        expect(Model.new.decorator_class?).to be_false
+      end
+    end
+
+    describe ".decorator_class?" do
+      it "returns true for decoratable model" do
+        expect(Product.decorator_class?).to be_true
+      end
+
+      it "returns false for non-decoratable model" do
+        expect(Model.decorator_class?).to be_false
+      end
+    end
+
     describe "#decorator_class" do
       it "delegates to .decorator_class" do
         product = Product.new