Add ActiveRecord::Base#invalid? as the opposite of #valid? [#2159 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activerecord/lib/active_record/validations.rb

@@ -1040,6 +1040,11 @@ def valid?
       errors.empty?
     end
 
+    # Performs the opposite of <tt>valid?</tt>. Returns true if errors were added, false otherwise.
+    def invalid?
+      !valid?
+    end
+
     # Returns the Errors object that holds all information about attribute error messages.
     def errors
       @errors ||= Errors.new(self)

activerecord/test/cases/validations_test.rb

@@ -170,7 +170,7 @@ def test_create_with_exceptions_using_scope_and_empty_attributes
         assert_equal person.first_name, "Mary", "should be ok when no attributes are passed to create!"
       end
     end
- end
+  end
 
   def test_single_error_per_attr_iteration
     r = Reply.new
@@ -1430,6 +1430,17 @@ def test_validation_order
      assert_equal "can't be blank", t.errors.on("title").first
   end
 
+  def test_invalid_should_be_the_opposite_of_valid
+    Topic.validates_presence_of :title
+
+    t = Topic.new
+    assert t.invalid?
+    assert t.errors.invalid?(:title)
+
+    t.title = 'Things are going to change'
+    assert !t.invalid?
+  end
+
   # previous implementation of validates_presence_of eval'd the
   # string with the wrong binding, this regression test is to
   # ensure that it works correctly