feat: undead-buffers: Add `cj/make-buffer-undead` function and tests

Introduce a new function `cj/make-buffer-undead` that appends a
buffer name to the `cj/undead-buffer-list`, preventing it from being
killed. This comes along with a suite of tests to check various
scenarios and edge cases for handling undead buffers.

Additionally, add tests for related functions:
`cj/kill-buffer-or-bury-alive`, `cj/kill-buffer-and-window`, and
others to ensure they correctly manage buffers, particularly with
undead-status considerations.

Refactor `undead-buffer-list` naming for consistency and clarity in
the module.

1 files changed, 106 insertions, 0 deletions

diff --git a/tests/test-undead-buffers-undead-buffer-p.el b/tests/test-undead-buffers-undead-buffer-p.el
new file mode 100644
index 00000000..107256c9
--- /dev/null
+++ b/tests/test-undead-buffers-undead-buffer-p.el
@@ -0,0 +1,106 @@
+;;; test-undead-buffers-undead-buffer-p.el --- Tests for cj/undead-buffer-p -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/undead-buffer-p function from undead-buffers.el
+
+;;; Code:
+
+(require 'ert)
+(require 'undead-buffers)
+(require 'testutil-general)
+
+;;; Setup and Teardown
+
+(defun test-undead-buffer-p-setup ()
+  "Setup for undead-buffer-p tests."
+  (cj/create-test-base-dir))
+
+(defun test-undead-buffer-p-teardown ()
+  "Teardown for undead-buffer-p tests."
+  (cj/delete-test-base-dir))
+
+;;; Normal Cases
+
+(ert-deftest test-undead-buffer-p-modified-file-buffer-should-return-true ()
+  "A modified file-backed buffer not in undead list should return t."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (let* ((file (cj/create-temp-test-file-with-content "test content"))
+             (buf (find-file-noselect file)))
+        (unwind-protect
+            (progn
+              (with-current-buffer buf
+                (insert "more content")
+                (should (cj/undead-buffer-p))))
+          (when (buffer-live-p buf)
+            (set-buffer-modified-p nil)
+            (kill-buffer buf))))
+    (test-undead-buffer-p-teardown)))
+
+(ert-deftest test-undead-buffer-p-undead-modified-file-buffer-should-return-nil ()
+  "A modified file-backed undead buffer should return nil."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (let* ((orig (copy-sequence cj/undead-buffer-list))
+             (file (cj/create-temp-test-file-with-content "test content"))
+             (buf (find-file-noselect file)))
+        (unwind-protect
+            (progn
+              (add-to-list 'cj/undead-buffer-list (buffer-name buf))
+              (with-current-buffer buf
+                (insert "more content")
+                (should-not (cj/undead-buffer-p))))
+          (setq cj/undead-buffer-list orig)
+          (when (buffer-live-p buf)
+            (set-buffer-modified-p nil)
+            (kill-buffer buf))))
+    (test-undead-buffer-p-teardown)))
+
+(ert-deftest test-undead-buffer-p-scratch-buffer-should-return-nil ()
+  "The *scratch* buffer should return nil (it's undead)."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (with-current-buffer "*scratch*"
+        (should-not (cj/undead-buffer-p)))
+    (test-undead-buffer-p-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-undead-buffer-p-unmodified-file-buffer-should-return-nil ()
+  "An unmodified file buffer should return nil."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (let* ((file (cj/create-temp-test-file-with-content "test content"))
+             (buf (find-file-noselect file)))
+        (unwind-protect
+            (with-current-buffer buf
+              (should-not (cj/undead-buffer-p)))
+          (when (buffer-live-p buf)
+            (kill-buffer buf))))
+    (test-undead-buffer-p-teardown)))
+
+(ert-deftest test-undead-buffer-p-modified-buffer-without-file-should-return-nil ()
+  "A modified buffer without a backing file should return nil."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (let ((buf (generate-new-buffer "*test-no-file*")))
+        (unwind-protect
+            (with-current-buffer buf
+              (insert "content")
+              (set-buffer-modified-p t)
+              (should-not (cj/undead-buffer-p)))
+          (when (buffer-live-p buf)
+            (set-buffer-modified-p nil)
+            (kill-buffer buf))))
+    (test-undead-buffer-p-teardown)))
+
+(ert-deftest test-undead-buffer-p-temporary-buffer-should-return-nil ()
+  "A temporary buffer should return nil."
+  (test-undead-buffer-p-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (should-not (cj/undead-buffer-p)))
+    (test-undead-buffer-p-teardown)))
+
+(provide 'test-undead-buffers-undead-buffer-p)
+;;; test-undead-buffers-undead-buffer-p.el ends here