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diff --git a/test/src/terminal-tests.el b/test/src/terminal-tests.el
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+++ b/test/src/terminal-tests.el
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+;;; terminal-tests.el --- tests for terminal.c -*- lexical-binding: t -*-
+
+;; Copyright (C) 2026 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+
+(ert-deftest frame-initial-p ()
+  "Test `frame-initial-p' behavior."
+  (should-not (frame-initial-p t))
+  (should-not (frame-initial-p (current-buffer)))
+  (should-not (frame-initial-p (selected-window)))
+  ;; "Initial frame" implies "initial terminal", and
+  ;; no other terminal can have the initial frame.
+  (should-not (xor (equal (terminal-name) "initial_terminal")
+                   (frame-initial-p)))
+  ;; Initial frame implies its terminal is a termcap-like
+  ;; text-mode terminal.
+  (should (or (not (frame-initial-p))
+              (eq (terminal-live-p nil) t)))
+  ;; It similarly implies a termcap-like text-mode frame.
+  (should (or (not (frame-initial-p))
+              (eq (frame-live-p (selected-frame)) t)))
+  (dolist (ft (append '(nil) (frame-list) (terminal-list)))
+    (ert-info ((prin1-to-string ft) :prefix "Argument: ")
+      (should-not (xor (equal (terminal-name ft) "initial_terminal")
+                       (frame-initial-p ft)))
+      (should (or (not (frame-initial-p ft))
+                  (eq (terminal-live-p ft) t)))))
+  (cond (noninteractive
+         ;; Batch mode should have an initial frame.
+         (should (any #'frame-initial-p (frame-list)))
+         (should (any #'frame-initial-p (terminal-list))))
+        ((not (daemonp))
+         ;; Non-daemon interactive mode should have none.
+         (should-not (any #'frame-initial-p (frame-list)))
+         (should-not (any #'frame-initial-p (terminal-list))))))
+
+;;; terminal-tests.el ends here