The following sample codes are not valid for the listed services but should allow basic testing of an authenticator application. Clicking on a QR code image will display just that code so it is easier to scan without interference from the other codes.
You can use this site to generate more QR codes as needed. It will also let you verify the produced codes against its own calculated code.
Acme Co (jdoe@example.com)
Amazon (jdoe@gmail.com)
DropBox (jdoe@gmail.com)
GitHub (jdoe@gmail.com)
Google (jdoe@gmail.com)
Reddit (jdoe@gmail.com)
Slack (jdoe@gmail.com)