diff --git a/test/difftastic-next-file.erts b/test/difftastic-next-file.erts
new file mode 100644
index 0000000..b73ef66
--- /dev/null
+++ b/test/difftastic-next-file.erts
@@ -0,0 +1,348 @@
+Code: difftastic-next-file
+
+Name: difftastic-next-file:file-wo-chunks-to-file-wo-chunks-1
+Point-Char: |
+=-=
+|difftastic.el --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:file-wo-chunks-to-file-wo-chunks-2
+Point-Char: |
+=-=
+difftastic.el| --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:file-wo-chunks-to-file-wo-chunks-3
+Point-Char: |
+=-=
+difftastic.el --- Emacs Lisp
+|1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-wo-chunks-1
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+|difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-wo-chunks-2
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Li|sp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-wo-chunks-3
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0|
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:first-chunk-to-file-wo-chunks-1
+Point-Char: |
+=-=
+|difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:first-chunk-to-file-wo-chunks-2
+Point-Char: |
+=-=
+difftastic.e|l --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:first-chunk-to-file-wo-chunks-3
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el| --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-with-chunks-1
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+|difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-with-chunks-2
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp|
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-with-chunks-3
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+|
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
+Name: difftastic-next-file:first-chunk-to-file-with-chunks-1
+Point-Char: |
+=-=
+|difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-with-chunks-2
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Ema|cs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
+
+Name: difftastic-next-file:last-chunk-to-file-with-chunks-3
+Point-Char: |
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for |difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=
+difftastic.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-
+
+difftastic.el --- 2/2 --- Emacs Lisp
+9 ;; Version: 0.0.0
+
+|test/difftastic.t.el --- 1/2 --- Emacs Lisp
+1 ;;; difftastic.t.el --- Tests for difftastic        -*- lexical-binding: t; -*-
+
+test/difftastic.t.el --- 2/2 --- Emacs Lisp
+5 (require 'difftastic)
+=-=-=
diff --git a/test/difftastic.t.el b/test/difftastic.t.el
index 49279d2..1ea975f 100644
--- a/test/difftastic.t.el
+++ b/test/difftastic.t.el
@@ -519,6 +519,36 @@
                     :type 'user-error)
       (should (equal (point-min) (point))))))
 
+(ert-deftest difftastic-next-file:erts-scenarios ()
+  (when (fboundp 'ert-test-erts-file) ;; since Emacs-29
+    (mocklet ((difftastic--get-languages => '("Text" "Emacs Lisp" "C++" "Java")))
+      (let ((file "difftastic-next-file.erts")
+            scenarios)
+        (should (or (file-exists-p file)
+                    (file-exists-p (format "test/%s" file))))
+        (setq scenarios (if (file-exists-p file)
+                            file
+                          (format "test/%s" file)))
+      (ert-test-erts-file scenarios)))))
+
+(ert-deftest difftastic-next-file:empty-buffer-error-signaled ()
+  (mocklet ((difftastic--get-languages => '("Text" "Emacs Lisp" "C++" "Java")))
+    (with-temp-buffer
+      (difftastic-mode)
+      (should-error (difftastic-next-file)
+                    :type 'user-error))))
+
+(ert-deftest difftastic-next-file:last-chunk-error-signaled ()
+  (mocklet ((difftastic--get-languages => '("Text" "Emacs Lisp" "C++" "Java")))
+    (with-temp-buffer
+      (insert "difftastic.el --- Emacs Lisp
+1 ;;; difftastic.el --- Wrapper for difftastic        -*- lexical-binding: t; -*-")
+      (difftastic-mode)
+      (goto-char (point-min))
+      (should-error (difftastic-next-file)
+                    :type 'user-error)
+      (should (equal (point-min) (point))))))
+
 (ert-deftest difftastic-previous-chunk:erts-scenarios ()
   (when (fboundp 'ert-test-erts-file) ;; since Emacs-29
     (mocklet ((difftastic--get-languages => '("Text" "Emacs Lisp" "C++" "Java")))