Undef the defined negated matcher

Author: ka8725

spec/rspec/rails/matchers/send_email_spec.rb

@@ -35,7 +35,7 @@ def test_email
     }.to send_email
   end
 
-  it "with with to_not" do
+  it "with to_not" do
     expect {
       mailer.test_email.deliver_now
     }.to_not send_email(
@@ -119,7 +119,12 @@ def test_email
   end
 
   context "with a custom negated version defined" do
-    before { RSpec::Matchers.define_negated_matcher :not_send_email, :send_email }
+    around do |example|
+      RSpec::Matchers.define_negated_matcher :not_send_email, :send_email
+      example.run
+    ensure
+      undef not_send_email
+    end
 
     it "works with a negated version" do
       expect {