My suggestion for solving this depends on whether you use a default identity provider or a user-selected identity provider.

- If you use a default identity provider, you can remove the defaultIdentityProvider attribute from the SamlConfig element of your external-authentication-config.xml. The user will then be redirected to the login-view-id (specified in pages.xml) if she tries to access a page for which she needs to be logged in. On that page (which you need to create for that purpose) the user can be authenticated with built-in Seam authentication.

- If you don't use a default identity provider, you already have a login screen where the user can choose her identity provider. You could add an option on that screen to login with a development/test user (using built in Seam authentication: #{identity.login()}). That option is enabled only if the environment is a development or test environment.