Merge pull request #473 from backus/feature/add-limitations-to-readme

Add limitations section to README

README.md

@@ -73,6 +73,54 @@ To mutation test Rails models with rspec comment out ```require 'rspec/autorun'`
 RAILS_ENV=test bundle exec mutant -r ./config/environment --use rspec User
 ```
 
+Limitations
+-----------
+
+Mutant cannot emit mutations for...
+
+* methods defined within a closure.  For example, methods defined using `module_eval`, `class_eval`,
+  `define_method`, or `define_singleton_method`:
+
+    ```ruby
+    class Example
+      class_eval do
+        def example1
+        end
+      end
+
+      module_eval do
+        def example2
+        end
+      end
+
+      define_method(:example3) do
+      end
+
+      define_singleton_method(:example4) do
+      end
+    end
+    ```
+
+* singleton methods not defined on a constant or `self`
+
+    ```ruby
+    class Foo
+      def self.bar; end   # ok
+      def Foo.baz; end    # ok
+
+      myself = self
+      def myself.qux; end # cannot mutate
+    end
+    ```
+
+* methods defined with eval:
+
+    ```ruby
+    class Foo
+      class_eval('def bar; end') # cannot mutate
+    end
+    ```
+
 Mutation-Operators:
 -------------------