Implement #negated? in superclass

All current matchers follow the pattern of negative assertions matching
`assert_not_*` and `refute_*`. If we add a matcher where the negative
assertions do not match this pattern, the method can still be overwritten
in that subclass.

Author: bquorning

lib/rubocop/cop/rspec_rails/minitest_assertions.rb

@@ -44,7 +44,7 @@ def replaced(node)
             end
 
             def negated?(node)
-              raise NotImplementedError
+              node.method_name.start_with?('assert_not_', 'refute_')
             end
 
             def assertion
@@ -68,10 +68,6 @@ def self.match(expected, actual, failure_message)
               new(expected, actual, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_equal)
-            end
-
             def assertion
               "eq(#{@expected})"
             end
@@ -93,10 +89,6 @@ def self.match(expected, actual, failure_message)
               new(expected, actual, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_instance_of)
-            end
-
             def assertion
               "be_an_instance_of(#{@expected})"
             end
@@ -118,10 +110,6 @@ def self.match(collection, expected, failure_message)
               new(expected, collection, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_includes)
-            end
-
             def assertion
               "include(#{@expected})"
             end
@@ -145,10 +133,6 @@ def self.match(subject, predicate, failure_message)
               new(predicate, subject, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_predicate)
-            end
-
             def assertion
               "be_#{@expected.delete_prefix(':').delete_suffix('?')}"
             end
@@ -169,10 +153,6 @@ def self.match(matcher, actual, failure_message)
               new(matcher, actual, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_match)
-            end
-
             def assertion
               "match(#{@expected})"
             end
@@ -194,10 +174,6 @@ def self.match(actual, failure_message)
               new(nil, actual, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_nil)
-            end
-
             def assertion
               'eq(nil)'
             end
@@ -219,10 +195,6 @@ def self.match(actual, failure_message)
               new(nil, actual, failure_message.first)
             end
 
-            def negated?(node)
-              !node.method?(:assert_empty)
-            end
-
             def assertion
               'be_empty'
             end