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+;;; test-jumper.el --- Tests for jumper.el -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for jumper.el - location navigation using registers.
+;;
+;; Testing approach:
+;; - Tests focus on internal `jumper--do-*` functions (pure business logic)
+;; - Interactive wrappers are thin UI layers and tested minimally
+;; - Each test is isolated with setup/teardown to reset global state
+;; - Tests verify return values, not user messages
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-general)
+
+;; Add modules directory to load path
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+;; Load the module
+(require 'jumper)
+
+;;; Test Utilities
+
+(defvar test-jumper--original-registers nil
+  "Backup of jumper registers before test.")
+
+(defvar test-jumper--original-index nil
+  "Backup of jumper index before test.")
+
+(defun test-jumper-setup ()
+  "Reset jumper state before each test."
+  ;; Backup current state
+  (setq test-jumper--original-registers jumper--registers)
+  (setq test-jumper--original-index jumper--next-index)
+  ;; Reset to clean state
+  (setq jumper--registers (make-vector jumper-max-locations nil))
+  (setq jumper--next-index 0))
+
+(defun test-jumper-teardown ()
+  "Restore jumper state after each test."
+  (setq jumper--registers test-jumper--original-registers)
+  (setq jumper--next-index test-jumper--original-index))
+
+;;; Normal Cases - Store Location
+
+(ert-deftest test-jumper-store-first-location ()
+  "Should store first location and return register character."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test content")
+    (goto-char (point-min))
+    (let ((result (jumper--do-store-location)))
+      (should (= result ?0))
+      (should (= jumper--next-index 1))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-store-multiple-locations ()
+  "Should store multiple locations in sequence."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (should (= (jumper--do-store-location) ?0))
+    (forward-line 1)
+    (should (= (jumper--do-store-location) ?1))
+    (forward-line 1)
+    (should (= (jumper--do-store-location) ?2))
+    (should (= jumper--next-index 3)))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-store-duplicate-location ()
+  "Should detect and reject duplicate locations."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test content")
+    (goto-char (point-min))
+    (should (= (jumper--do-store-location) ?0))
+    (should (eq (jumper--do-store-location) 'already-exists))
+    (should (= jumper--next-index 1)))
+  (test-jumper-teardown))
+
+;;; Normal Cases - Jump to Location
+
+(ert-deftest test-jumper-jump-to-stored-location ()
+  "Should jump to a previously stored location."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (goto-char (point-max))
+    (let ((result (jumper--do-jump-to-location 0)))
+      (should (eq result 'jumped))
+      (should (= (point) (point-min)))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-jump-toggle-with-single-location ()
+  "Should toggle between current and stored location."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    ;; Move away
+    (goto-char (point-max))
+    ;; Toggle should jump back
+    (let ((result (jumper--do-jump-to-location nil)))
+      (should (eq result 'jumped))
+      (should (= (point) (point-min)))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-jump-already-at-location ()
+  "Should detect when already at the only stored location."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    ;; Try to toggle while at the location
+    (let ((result (jumper--do-jump-to-location nil)))
+      (should (eq result 'already-there))))
+  (test-jumper-teardown))
+
+;;; Normal Cases - Remove Location
+
+(ert-deftest test-jumper-remove-location ()
+  "Should remove a stored location."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test content")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (let ((result (jumper--do-remove-location 0)))
+      (should (eq result t))
+      (should (= jumper--next-index 0))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-remove-reorders-registers ()
+  "Should reorder registers after removal from middle."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (jumper--do-store-location)  ; Register 0
+    (forward-line 1)
+    (jumper--do-store-location)  ; Register 1
+    (forward-line 1)
+    (jumper--do-store-location)  ; Register 2
+    ;; Remove middle (index 1)
+    (jumper--do-remove-location 1)
+    (should (= jumper--next-index 2))
+    ;; What was at index 2 should now be at index 1
+    (should (= (aref jumper--registers 1) ?2)))
+  (test-jumper-teardown))
+
+;;; Boundary Cases - Store Location
+
+(ert-deftest test-jumper-store-at-capacity ()
+  "Should successfully store location at maximum capacity."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test content")
+    (goto-char (point-min))
+    ;; Fill to capacity
+    (dotimes (i jumper-max-locations)
+      (forward-char 1)
+      (should (= (jumper--do-store-location) (+ ?0 i))))
+    (should (= jumper--next-index jumper-max-locations)))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-store-when-full ()
+  "Should return 'no-space when all registers are full."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "01234567890123456789")
+    (goto-char (point-min))
+    ;; Fill to capacity
+    (dotimes (i jumper-max-locations)
+      (forward-char 1)
+      (jumper--do-store-location))
+    ;; Try to store one more
+    (forward-char 1)
+    (should (eq (jumper--do-store-location) 'no-space))
+    (should (= jumper--next-index jumper-max-locations)))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-store-in-different-buffers ()
+  "Should store locations across different buffers."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "buffer 1")
+    (goto-char (point-min))
+    (should (= (jumper--do-store-location) ?0))
+    (with-temp-buffer
+      (insert "buffer 2")
+      (goto-char (point-min))
+      (should (= (jumper--do-store-location) ?1))
+      (should (= jumper--next-index 2))))
+  (test-jumper-teardown))
+
+;;; Boundary Cases - Jump to Location
+
+(ert-deftest test-jumper-jump-with-no-locations ()
+  "Should return 'no-locations when nothing is stored."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test")
+    (let ((result (jumper--do-jump-to-location 0)))
+      (should (eq result 'no-locations))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-jump-to-first-location ()
+  "Should jump to location at index 0."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (forward-line 1)
+    (jumper--do-store-location)
+    (goto-char (point-max))
+    (jumper--do-jump-to-location 0)
+    (should (= (point) (point-min))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-jump-to-last-location ()
+  "Should jump to last location (register 'z)."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (let ((line2-pos (line-beginning-position 2)))
+      (goto-char line2-pos)
+      ;; Jump to location 0 (this stores current location in 'z)
+      (jumper--do-jump-to-location 0)
+      (should (= (point) (point-min)))
+      ;; Jump to last location should go back to line 2
+      (let ((result (jumper--do-jump-to-location -1)))
+        (should (eq result 'jumped))
+        (should (= (point) line2-pos)))))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-jump-to-max-index ()
+  "Should jump to location at maximum index."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "0123456789012345678")
+    (goto-char (point-min))
+    ;; Store at all positions
+    (dotimes (i jumper-max-locations)
+      (forward-char 1)
+      (jumper--do-store-location))
+    (goto-char (point-min))
+    ;; Jump to last one (index 9, which is at position 10)
+    (jumper--do-jump-to-location (1- jumper-max-locations))
+    (should (= (point) (1+ jumper-max-locations))))
+  (test-jumper-teardown))
+
+;;; Boundary Cases - Remove Location
+
+(ert-deftest test-jumper-remove-first-location ()
+  "Should remove location at index 0."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (forward-line 1)
+    (jumper--do-store-location)
+    (jumper--do-remove-location 0)
+    (should (= jumper--next-index 1))
+    ;; What was at index 1 should now be at index 0
+    (should (= (aref jumper--registers 0) ?1)))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-remove-last-location ()
+  "Should remove location at last index."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "line 1\nline 2\nline 3")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (forward-line 1)
+    (jumper--do-store-location)
+    (forward-line 1)
+    (jumper--do-store-location)
+    (jumper--do-remove-location 2)
+    (should (= jumper--next-index 2)))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-remove-with-cancel ()
+  "Should return 'cancelled when index is -1."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (let ((result (jumper--do-remove-location -1)))
+      (should (eq result 'cancelled))
+      (should (= jumper--next-index 1))))
+  (test-jumper-teardown))
+
+;;; Error Cases
+
+(ert-deftest test-jumper-remove-when-empty ()
+  "Should return 'no-locations when removing from empty list."
+  (test-jumper-setup)
+  (let ((result (jumper--do-remove-location 0)))
+    (should (eq result 'no-locations)))
+  (test-jumper-teardown))
+
+;;; Helper Function Tests
+
+(ert-deftest test-jumper-location-key-format ()
+  "Should generate unique location keys."
+  (with-temp-buffer
+    (insert "line 1\nline 2")
+    (goto-char (point-min))
+    (let ((key1 (jumper--location-key)))
+      (forward-line 1)
+      (let ((key2 (jumper--location-key)))
+        (should-not (string= key1 key2))
+        ;; Keys should contain buffer name and position info
+        (should (string-match-p ":" key1))
+        (should (string-match-p ":" key2))))))
+
+(ert-deftest test-jumper-register-available-p ()
+  "Should correctly report register availability."
+  (test-jumper-setup)
+  (should (jumper--register-available-p))
+  ;; Fill to capacity
+  (setq jumper--next-index jumper-max-locations)
+  (should-not (jumper--register-available-p))
+  (test-jumper-teardown))
+
+(ert-deftest test-jumper-format-location ()
+  "Should format location for display."
+  (test-jumper-setup)
+  (with-temp-buffer
+    (insert "test line with some content")
+    (goto-char (point-min))
+    (jumper--do-store-location)
+    (let ((formatted (jumper--format-location 0)))
+      (should formatted)
+      (should (string-match-p "\\[0\\]" formatted))
+      (should (string-match-p "test line" formatted))))
+  (test-jumper-teardown))
+
+(provide 'test-jumper)
+;;; test-jumper.el ends here