1 files changed, 146 insertions, 0 deletions
diff --git a/tests/test-custom-whitespace-ensure-single-blank.el b/tests/test-custom-whitespace-ensure-single-blank.el
new file mode 100644
index 00000000..7cd03e79
--- /dev/null
+++ b/tests/test-custom-whitespace-ensure-single-blank.el
@@ -0,0 +1,146 @@
+;;; test-custom-whitespace-ensure-single-blank.el --- Tests for cj/--ensure-single-blank-line -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/--ensure-single-blank-line function from custom-whitespace.el
+;;
+;; This function collapses multiple consecutive blank lines to exactly one blank line.
+;; Different from delete-blank-lines which removes ALL blank lines, this function
+;; preserves blank lines but ensures no more than one blank line appears consecutively.
+;;
+;; A blank line is defined as a line containing only whitespace (spaces, tabs) or nothing.
+;; Uses the regexp (^[[:space:]]*$\n){2,} to match 2+ consecutive blank lines.
+;;
+;; We test the NON-INTERACTIVE implementation (cj/--ensure-single-blank-line)
+;; to avoid mocking user prompts. This follows our testing best practice
+;; of separating business logic from UI interaction.
+
+;;; 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.")
+
+;; Now load the actual production module
+(require 'custom-whitespace)
+
+;;; Test Helpers
+
+(defun test-ensure-single-blank-line (input-text)
+  "Test cj/--ensure-single-blank-line on INPUT-TEXT.
+Returns the buffer string after operation."
+  (with-temp-buffer
+    (insert input-text)
+    (cj/--ensure-single-blank-line (point-min) (point-max))
+    (buffer-string)))
+
+;;; Normal Cases
+
+(ert-deftest test-ensure-single-blank-two-blanks ()
+  "Should collapse two blank lines to one."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-three-blanks ()
+  "Should collapse three blank lines to one."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\n\nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-many-blanks ()
+  "Should collapse many blank lines to one."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\n\n\n\n\nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-preserve-single ()
+  "Should preserve single blank lines (no-op)."
+  (let ((result (test-ensure-single-blank-line "line1\n\nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-multiple-groups ()
+  "Should handle multiple groups of consecutive blanks."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\nline2\n\n\n\nline3")))
+    (should (string= result "line1\n\nline2\n\nline3"))))
+
+(ert-deftest test-ensure-single-blank-blanks-with-spaces ()
+  "Should handle blank lines with spaces only."
+  (let ((result (test-ensure-single-blank-line "line1\n   \n   \nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-blanks-with-tabs ()
+  "Should handle blank lines with tabs only."
+  (let ((result (test-ensure-single-blank-line "line1\n\t\t\n\t\t\nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-mixed-whitespace ()
+  "Should handle blank lines with mixed whitespace."
+  (let ((result (test-ensure-single-blank-line "line1\n \t \n  \t  \nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-ensure-single-blank-no-blanks ()
+  "Should handle text with no blank lines (no-op)."
+  (let ((result (test-ensure-single-blank-line "line1\nline2\nline3")))
+    (should (string= result "line1\nline2\nline3"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-ensure-single-blank-empty-string ()
+  "Should handle empty string."
+  (let ((result (test-ensure-single-blank-line "")))
+    (should (string= result ""))))
+
+(ert-deftest test-ensure-single-blank-only-blanks ()
+  "Should collapse many blank lines to one blank line."
+  (let ((result (test-ensure-single-blank-line "\n\n\n\n")))
+    (should (string= result "\n\n"))))
+
+(ert-deftest test-ensure-single-blank-at-start ()
+  "Should collapse multiple blank lines at start to one."
+  (let ((result (test-ensure-single-blank-line "\n\n\nline1")))
+    (should (string= result "\n\nline1"))))
+
+(ert-deftest test-ensure-single-blank-at-end ()
+  "Should collapse multiple blank lines at end to one."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\n")))
+    (should (string= result "line1\n\n"))))
+
+(ert-deftest test-ensure-single-blank-single-line ()
+  "Should handle single line (no-op)."
+  (let ((result (test-ensure-single-blank-line "line1")))
+    (should (string= result "line1"))))
+
+(ert-deftest test-ensure-single-blank-complex-structure ()
+  "Should handle complex mix of content and blanks."
+  (let ((result (test-ensure-single-blank-line "line1\n\n\nline2\nline3\n\n\n\nline4")))
+    (should (string= result "line1\n\nline2\nline3\n\nline4"))))
+
+(ert-deftest test-ensure-single-blank-preserves-content ()
+  "Should not modify lines with content."
+  (let ((result (test-ensure-single-blank-line "  line1  \n\n\n  line2  ")))
+    (should (string= result "  line1  \n\n  line2  "))))
+
+;;; Error Cases
+
+(ert-deftest test-ensure-single-blank-start-greater-than-end ()
+  "Should error when start > end."
+  (should-error
+   (with-temp-buffer
+     (insert "line1\n\n\nline2")
+     (cj/--ensure-single-blank-line (point-max) (point-min)))
+   :type 'error))
+
+(ert-deftest test-ensure-single-blank-empty-region ()
+  "Should handle empty region (start == end) without error."
+  (with-temp-buffer
+    (insert "line1\n\n\nline2")
+    (let ((pos (/ (+ (point-min) (point-max)) 2)))
+      (cj/--ensure-single-blank-line pos pos)
+      ;; Should complete without error
+      (should (string-match-p "line1" (buffer-string))))))
+
+(provide 'test-custom-whitespace-ensure-single-blank)
+;;; test-custom-whitespace-ensure-single-blank.el ends here