Test and fix for call_through w/ instance methods

lib/spy/subroutine.rb

@@ -135,13 +135,29 @@ def and_yield(*args)
     # tells the spy to call the original method
     # @return [self]
     def and_call_through
-      @plan = Proc.new do |*args, &block|
-        if original_method
-          original_method.call(*args, &block)
-        else
-          base_object.send(:method_missing, method_name, *args, &block)
+      if @base_object.is_a? Class
+        @plan = Proc.new do |object, *args, &block|
+          if original_method
+            if original_method.is_a? UnboundMethod
+              bound_method = original_method.bind(object)
+              bound_method.call(*args, &block)
+            else
+              original_method.call(*args, &block)
+            end
+          else
+            base_object.send(:method_missing, method_name, *args, &block)
+          end
+        end
+      else
+        @plan = Proc.new do |*args, &block|
+          if original_method
+            original_method.call(*args, &block)
+          else
+            base_object.send(:method_missing, method_name, *args, &block)
+          end
         end
       end
+
       self
     end
 
@@ -202,10 +218,18 @@ def has_been_called_with?(*args)
     # method.
     def invoke(object, args, block, called_from)
       check_arity!(args.size)
-      result = if @plan
-                 check_for_too_many_arguments!(@plan)
-                 @plan.call(*args, &block)
-               end
+
+      if base_object.is_a? Class
+        result = if @plan
+                   check_for_too_many_arguments!(@plan)
+                   @plan.call(object, *args, &block)
+                 end
+      else
+        result = if @plan
+                   check_for_too_many_arguments!(@plan)
+                   @plan.call(*args, &block)
+                 end
+      end
     ensure
       calls << CallLog.new(object, called_from, args, block, result)
     end
@@ -273,6 +297,8 @@ def check_for_too_many_arguments!(block)
       min_arity = block.arity
       min_arity = min_arity.abs - 1 if min_arity < 0
 
+      min_arity -=1 if base_object.is_a? Class # Instance-method procs take an extra param for receiving object
+
       if min_arity > arity_range.max
         raise ArgumentError.new("block requires #{min_arity} arguments while original_method require a maximum of #{arity_range.max}")
       end

test/integration/test_instance_method.rb

@@ -17,6 +17,12 @@ def teardown
     Spy::Agency.instance.dissolve!
   end
 
+  def test_call_through_with_instance_method
+    Spy.on_instance_method(Foo, :bar).and_call_through
+    assert_equal "foobar", Foo.new.bar
+    Spy.off_instance_method(Foo, :bar)
+  end
+
   def test_it_overides_all_methods
     assert_equal Foo.new.bar, "foobar"
     spy = Spy.on_instance_method(Foo, bar: "timshel")