add APIToken expiration mailer

spec/mailers/previews/api_token_mailer_preview.rb

@@ -0,0 +1,23 @@
+class APITokenMailerPreview < ActionMailer::Preview
+  def expiration
+    APITokenMailer.expiration(api_token)
+  end
+
+  private
+
+  def api_token
+    APIToken.new(
+      administrateur: administrateur,
+      expires_at: 1.week.from_now,
+      name: 'My API token'
+    )
+  end
+
+  def administrateur
+    Administrateur.new(user:)
+  end
+
+  def user
+    User.new(email: 'admin@a.com')
+  end
+end