Merge pull request #421 from xaviershay/issue-392

Verifying null objects only respond to defined methods.

Changelog.md

@@ -26,6 +26,8 @@ Enhancements:
 * Yield the receiver to `any_instance` implementation blocks (Sam Phippen).
 * Provide `instance_double` and `class_double` to create verifying doubles,
   ported from `rspec-fire` (Xavier Shay).
+* `as_null_object` on a verifying double only responds to defined methods
+  (Xavier Shay).
 * Improved performance of double creation, particularly those with many
   attributes. (Xavier Shay)
 * Default value of `transfer_nested_constants` option for constant stubbing can

lib/rspec/mocks/example_methods.rb

@@ -35,28 +35,28 @@ def double(*args)
       # @overload instance_double(doubled_class, stubs)
       # @param doubled_class [String, Class]
       # @param stubs [Hash] (optional) hash of message/return-value pairs
-      # @return InstanceVerifyingMock
+      # @return InstanceVerifyingDouble
       #
       # Constructs a test double against a specific class. If the given class
       # name has been loaded, only instance methods defined on the class are
       # allowed to be stubbed. In all other ways it behaves like a
       # [double](double).
       def instance_double(doubled_class, *args)
-        declare_verifying_double(InstanceVerifyingMock, doubled_class, *args)
+        declare_verifying_double(InstanceVerifyingDouble, doubled_class, *args)
       end
 
       # @overload class_double(doubled_class)
       # @overload class_double(doubled_class, stubs)
       # @param doubled_class [String, Module]
       # @param stubs [Hash] (optional) hash of message/return-value pairs
-      # @return ClassVerifyingMock
+      # @return ClassVerifyingDouble
       #
       # Constructs a test double against a specific class. If the given class
       # name has been loaded, only class methods defined on the class are
       # allowed to be stubbed. In all other ways it behaves like a
       # [double](double).
       def class_double(doubled_class, *args)
-        declare_verifying_double(ClassVerifyingMock, doubled_class, *args)
+        declare_verifying_double(ClassVerifyingDouble, doubled_class, *args)
       end
 
       # Disables warning messages about expectations being set on nil.

lib/rspec/mocks/verifying_double.rb

@@ -4,11 +4,22 @@
 module RSpec
   module Mocks
 
+    module VerifyingDouble
+      def method_missing(message, *args, &block)
+        # Null object conditional is an optimization. If not a null object,
+        # validity of method expectations will have been checked at definition
+        # time.
+        __mock_proxy.ensure_implemented(message) if null_object?
+        super
+      end
+    end
+
     # A mock providing a custom proxy that can verify the validity of any
     # method stubs or expectations against the public instance methods of the
     # given class.
-    class InstanceVerifyingMock
+    class InstanceVerifyingDouble
       include TestDouble
+      include VerifyingDouble
 
       def initialize(doubled_module, *args)
         @doubled_module = doubled_module
@@ -25,13 +36,14 @@ def __build_mock_proxy
       end
     end
 
-    # Similar to an InstanceVerifyingMock, except that it verifies against
+    # Similar to an InstanceVerifyingDouble, except that it verifies against
     # public methods of the given class (i.e. the "class methods").
     #
     # Module needs to be in the inheritance chain for transferring nested
     # constants to work.
-    class ClassVerifyingMock < Module
+    class ClassVerifyingDouble < Module
       include TestDouble
+      include VerifyingDouble
 
       def initialize(doubled_module, *args)
         @doubled_module = doubled_module

lib/rspec/mocks/verifying_proxy.rb

@@ -58,8 +58,6 @@ def method_double
         end
       end
 
-    protected
-
       def ensure_implemented(method_name)
         @doubled_module.when_loaded do |original_module|
           unless original_module.__send__(@method_checker, method_name)

spec/rspec/mocks/verifying_double_spec.rb

@@ -107,6 +107,13 @@ def prevents(&block)
             o = instance_double(LoadedClass, :defined_instance_method => 1)
             expect(o.defined_instance_method).to eq(1)
           end
+
+          it 'only allows defined methods for null objects' do
+            o = instance_double('LoadedClass').as_null_object
+
+            expect(o.defined_instance_method).to eq(o)
+            prevents { o.undefined_method }
+          end
         end
       end
 
@@ -186,6 +193,13 @@ def prevents(&block)
               expect(dbl1).to receive(:undefined_class_method)
             }
           end
+
+          it 'only allows defined methods for null objects' do
+            o = class_double('LoadedClass').as_null_object
+
+            expect(o.defined_class_method).to eq(o)
+            prevents { o.undefined_method }
+          end
         end
       end