test: Add unit tests for `join-line-or-region` and `join-paragraph`

Add comprehensive test cases for the `cj/join-line-or-region` and
`cj/join-paragraph` functions within the custom-line-paragraph
module. These tests cover normal, boundary, and error cases to
ensure the proper functionality of line and paragraph joining
features. They address various scenarios including line breaks,
whitespace, Unicode content, and cursor positioning, enhancing the
robustness of existing functionality.

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
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+++ 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