1 files changed, 427 insertions, 0 deletions
diff --git a/tests/test-custom-line-paragraph-join-line-or-region.el b/tests/test-custom-line-paragraph-join-line-or-region.el
new file mode 100644
index 00000000..674d4618
--- /dev/null
+++ b/tests/test-custom-line-paragraph-join-line-or-region.el
@@ -0,0 +1,427 @@
+;;; test-custom-line-paragraph-join-line-or-region.el --- Tests for cj/join-line-or-region -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/join-line-or-region function from custom-line-paragraph.el
+;;
+;; IMPORTANT NOTE ON REGION ACTIVATION IN BATCH MODE:
+;; When testing functions that use (use-region-p) in batch mode, you must
+;; explicitly activate the region. Unlike interactive Emacs, batch mode does
+;; not automatically activate regions when you set mark and point.
+;;
+;; To properly test region-based behavior in batch mode:
+;; 1. Enable transient-mark-mode: (transient-mark-mode 1)
+;; 2. Set mark and point as needed
+;; 3. Explicitly activate the mark: (activate-mark)
+;;
+;; Without these steps, (use-region-p) will return nil even when mark and
+;; point are set, causing the function to take the no-region code path.
+;; This is a common pitfall that junior developers may miss when writing
+;; ERT tests for region-aware commands.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-general)
+
+;; Add modules directory to load path
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+;; Stub dependencies before loading the module
+(defvar cj/custom-keymap (make-sparse-keymap)
+  "Stub keymap for testing.")
+
+;; Stub expand-region package
+(provide 'expand-region)
+
+;; Now load the actual production module
+(require 'custom-line-paragraph)
+
+;;; Setup and Teardown
+
+(defun test-join-line-or-region-setup ()
+  "Setup for join-line-or-region tests."
+  (cj/create-test-base-dir))
+
+(defun test-join-line-or-region-teardown ()
+  "Teardown for join-line-or-region tests."
+  (cj/delete-test-base-dir))
+
+;;; Normal Cases
+
+(ert-deftest test-join-line-or-region-no-region-joins-with-previous-line ()
+  "Without region, should join current line with previous line."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "line one line two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-no-region-adds-newline-after-join ()
+  "Without region, should add newline after joining."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-suffix-p "\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-with-region-joins-all-lines ()
+  "With region, should join all lines in region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "line one line two line three" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-with-region-adds-newline-at-end ()
+  "With region, should add newline at end."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-suffix-p "\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-preserves-text-content ()
+  "Should preserve all text content when joining."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "hello\nworld")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "hello.*world" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-removes-line-breaks-between-words ()
+  "Should remove line breaks and add spaces between words."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "hello\nworld")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "hello world" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-multiple-lines-in-region ()
+  "Should handle multiple lines in region correctly."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "one\ntwo\nthree\nfour\nfive")
+        (goto-char (point-min))
+        (forward-line 1)
+        (set-mark (point))
+        (forward-line 3)
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "two three four" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-join-line-or-region-on-first-line-no-region-does-nothing-except-newline ()
+  "On first line without region, should only add newline."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "only line")
+        (goto-char (point-min))
+        (cj/join-line-or-region)
+        (should (string= "only line\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-empty-lines-in-region ()
+  "Should handle empty lines in region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\n\nline three")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "line one.*line three" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-single-line-region ()
+  "Should handle single-line region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "only line")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string= "only line\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-region-with-only-whitespace-lines ()
+  "Should handle region with only whitespace lines."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "   \n   \n   ")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (stringp (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-lines-with-leading-whitespace ()
+  "Should handle lines with leading whitespace."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\n  line two")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "line one.*line two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-lines-with-trailing-whitespace ()
+  "Should handle lines with trailing whitespace."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one  \nline two")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "line one.*line two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-lines-with-tabs ()
+  "Should handle lines with tab characters."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line\tone\nline\ttwo")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "line.*one.*line.*two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-lines-with-mixed-whitespace ()
+  "Should handle lines with mixed whitespace."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "  line \t one  \n\t line  two\t")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "line.*one.*line.*two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-very-long-lines ()
+  "Should handle very long lines."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (let ((long-line (make-string 5000 ?x)))
+          (insert long-line "\n" long-line)
+          (goto-char (point-max))
+          (cj/join-line-or-region)
+          (should (= (length (buffer-string)) (+ (* 2 5000) 1 1)))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-unicode-characters ()
+  "Should handle unicode characters."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "café\nnaïve")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "café.*naïve" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-emoji-content ()
+  "Should handle emoji content."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "hello 👋\nworld 🌍")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "hello 👋.*world 🌍" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-rtl-text ()
+  "Should handle RTL text."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "مرحبا\nعالم")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string-match-p "مرحبا.*عالم" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-region-at-buffer-start ()
+  "Should handle region starting at buffer beginning."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (goto-char (point-min))
+        (set-mark (point))
+        (forward-line 2)
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "line one line two" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-region-at-buffer-end ()
+  "Should handle region ending at buffer end."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (goto-char (point-min))
+        (forward-line 1)
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "line two line three" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-entire-buffer-as-region ()
+  "Should handle entire buffer selected as region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "one\ntwo\nthree")
+        (transient-mark-mode 1)
+        (mark-whole-buffer)
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "one two three" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-single-character-lines ()
+  "Should handle single character lines."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "a\nb\nc")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (activate-mark)
+        (cj/join-line-or-region)
+        (should (string-match-p "a b c" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-cursor-position-after-no-region ()
+  "Cursor should be at end after joining without region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (= (point) (point-max))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-cursor-position-after-region ()
+  "Cursor should be at region end marker after joining region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (goto-char (point-min))
+        (set-mark (point))
+        (goto-char (point-max))
+        (let ((end-pos (point)))
+          (activate-mark)
+          (cj/join-line-or-region)
+          ;; Point should be near the original end position
+          (should (>= (point) (- end-pos 10)))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-marker-validity-after-operation ()
+  "Marker should remain valid after operation."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two\nline three")
+        (let ((marker (set-marker (make-marker) (point-min))))
+          (goto-char (point-min))
+          (set-mark (point))
+          (goto-char (point-max))
+          (activate-mark)
+          (cj/join-line-or-region)
+          (should (marker-position marker))))
+    (test-join-line-or-region-teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-join-line-or-region-empty-buffer-no-region ()
+  "Should handle empty buffer gracefully without region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (cj/join-line-or-region)
+        (should (string= "\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-empty-buffer-with-region ()
+  "Should handle empty buffer gracefully with region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (mark-whole-buffer)
+        (cj/join-line-or-region)
+        (should (string= "\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-single-line-buffer-no-region ()
+  "Should handle single line buffer without region."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "only line")
+        (goto-char (point-max))
+        (cj/join-line-or-region)
+        (should (string= "only line\n" (buffer-string))))
+    (test-join-line-or-region-teardown)))
+
+(ert-deftest test-join-line-or-region-read-only-buffer-should-error ()
+  "Should error when attempting to modify read-only buffer."
+  (test-join-line-or-region-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "line one\nline two")
+        (goto-char (point-max))
+        (read-only-mode 1)
+        (should-error (cj/join-line-or-region)))
+    (test-join-line-or-region-teardown)))
+
+(provide 'test-custom-line-paragraph-join-line-or-region)
+;;; test-custom-line-paragraph-join-line-or-region.el ends here