Add anchors to spec DNS stubs

spec/support/helpers/dns_helpers.rb

@@ -17,13 +17,13 @@ module DnsHelpers
   end
 
   def stub_invalid_dns!
-    allow(Addrinfo).to receive(:getaddrinfo).with(/foobar\.\w|(\d{1,3}\.){4,}\d{1,3}/i, anything, nil, :STREAM) do
+    allow(Addrinfo).to receive(:getaddrinfo).with(/\Afoobar\.\w|(\d{1,3}\.){4,}\d{1,3}\z/i, anything, nil, :STREAM) do
       raise SocketError.new("getaddrinfo: Name or service not known")
     end
   end
 
   def permit_local_dns!
-    local_addresses = /(127|10)\.0\.0\.\d{1,3}|(192\.168|172\.16)\.\d{1,3}\.\d{1,3}|0\.0\.0\.0|localhost/i
+    local_addresses = /\A(127|10)\.0\.0\.\d{1,3}|(192\.168|172\.16)\.\d{1,3}\.\d{1,3}|0\.0\.0\.0|localhost\z/i
     allow(Addrinfo).to receive(:getaddrinfo).with(local_addresses, anything, nil, :STREAM).and_call_original
     allow(Addrinfo).to receive(:getaddrinfo).with(local_addresses, anything, nil, :STREAM, anything, anything).and_call_original
   end