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+;;; test-video-audio-recording-detect-system-device.el --- Tests for cj/recording-detect-system-device -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for cj/recording-detect-system-device function.
+;; Tests auto-detection of system audio monitor device from pactl output.
+;; Mocks shell-command-to-string to test regex matching logic.
+;;
+;; NOTE: This function works correctly - returns the full device name ending in .monitor.
+;; The regex \\([^\t\n]+\\.monitor\\) matches any non-tab/newline chars ending with .monitor,
+;; which correctly captures the device name field from pactl output.
+;;
+;; This function may not be actively used (parse-sources is preferred).
+;; Tests document current behavior to catch regressions.
+
+;;; Code:
+
+(require 'ert)
+
+;; Stub dependencies before loading the module
+(defvar cj/custom-keymap (make-sparse-keymap)
+  "Stub keymap for testing.")
+
+;; Now load the actual production module
+(require 'video-audio-recording)
+
+;;; Normal Cases
+
+(ert-deftest test-video-audio-recording-detect-system-device-normal-built-in-monitor-found ()
+  "Test detection of built-in system audio monitor.
+Returns full device name."
+  (let ((output "49\talsa_output.pci-0000_00_1f.3.analog-stereo.monitor\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n50\talsa_input.pci-0000_00_1f.3.analog-stereo\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (stringp result))
+        (should (equal "alsa_output.pci-0000_00_1f.3.analog-stereo.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-normal-usb-monitor-found ()
+  "Test detection of USB system audio monitor."
+  (let ((output "99\talsa_output.usb-0b0e_Jabra_SPEAK_510_USB_1C48F9C067D5020A00-00.analog-stereo.monitor\tPipeWire\ts16le 2ch 48000Hz\tSUSPENDED\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (stringp result))
+        (should (equal "alsa_output.usb-0b0e_Jabra_SPEAK_510_USB_1C48F9C067D5020A00-00.analog-stereo.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-normal-bluetooth-monitor-found ()
+  "Test detection of Bluetooth monitor device."
+  (let ((output "81\tbluez_output.00_1B_66_C0_91_6D.1.monitor\tPipeWire\ts24le 2ch 48000Hz\tRUNNING\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (stringp result))
+        (should (equal "bluez_output.00_1B_66_C0_91_6D.1.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-normal-first-match-returned ()
+  "Test that first matching monitor is returned when multiple exist."
+  (let ((output (concat "49\talsa_output.pci-0000_00_1f.3.analog-stereo.monitor\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"
+                        "81\tbluez_output.00_1B_66_C0_91_6D.1.monitor\tPipeWire\ts24le 2ch 48000Hz\tRUNNING\n"
+                        "99\talsa_output.usb-device.monitor\tPipeWire\ts16le 2ch 48000Hz\tSUSPENDED\n")))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        ;; Returns first monitor device name
+        (should (equal "alsa_output.pci-0000_00_1f.3.analog-stereo.monitor" result))))))
+
+;;; Boundary Cases
+
+(ert-deftest test-video-audio-recording-detect-system-device-boundary-empty-output-returns-nil ()
+  "Test that empty output returns nil."
+  (cl-letf (((symbol-function 'shell-command-to-string)
+             (lambda (_cmd) "")))
+    (let ((result (cj/recording-detect-system-device)))
+      (should (null result)))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-boundary-only-inputs-returns-nil ()
+  "Test that output with only input devices (no monitors) returns nil."
+  (let ((output (concat "50\talsa_input.pci-0000_00_1f.3.analog-stereo\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"
+                        "79\tbluez_input.00:1B:66:C0:91:6D\tPipeWire\tfloat32le 1ch 48000Hz\tSUSPENDED\n")))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (null result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-boundary-whitespace-only-returns-nil ()
+  "Test that whitespace-only output returns nil."
+  (cl-letf (((symbol-function 'shell-command-to-string)
+             (lambda (_cmd) "  \n\t\n  ")))
+    (let ((result (cj/recording-detect-system-device)))
+      (should (null result)))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-boundary-monitor-different-states ()
+  "Test that monitors in different states are all matched."
+  (let ((output "81\tbluez_output.00_1B_66_C0_91_6D.1.monitor\tPipeWire\ts24le 2ch 48000Hz\tRUNNING\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        ;; Should match regardless of state (RUNNING, SUSPENDED, IDLE)
+        (should (equal "bluez_output.00_1B_66_C0_91_6D.1.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-boundary-case-insensitive-monitor ()
+  "Test that regex is case-insensitive for '.monitor' suffix.
+Documents that .MONITOR (uppercase) also matches."
+  (let ((output "49\talsa_output.pci-0000_00_1f.3.analog-stereo.MONITOR\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        ;; Case-insensitive: .MONITOR matches
+        (should (equal "alsa_output.pci-0000_00_1f.3.analog-stereo.MONITOR" result))))))
+
+;;; Error Cases
+
+(ert-deftest test-video-audio-recording-detect-system-device-error-malformed-output-returns-nil ()
+  "Test that malformed output returns nil."
+  (let ((output "This is not valid pactl output\nRandom text here\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (null result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-error-partial-monitor-matches ()
+  "Test that device with .monitor in middle partially matches (documents quirk).
+The regex matches up to first .monitor occurrence, even if not at end of device name."
+  (let ((output "50\talsa_input.monitor-device.analog-stereo\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        ;; QUIRK: Matches partial string "alsa_input.monitor"
+        (should (equal "alsa_input.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-error-incomplete-line ()
+  "Test that incomplete lines with .monitor are still matched."
+  (let ((output "49\tincomplete-line.monitor\n"))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        ;; Should match device name ending in .monitor
+        (should (equal "incomplete-line.monitor" result))))))
+
+(ert-deftest test-video-audio-recording-detect-system-device-error-mixed-valid-invalid ()
+  "Test that mix of valid and invalid lines returns first valid monitor."
+  (let ((output (concat "invalid line without tabs\n"
+                        "49\talsa_output.pci-0000_00_1f.3.analog-stereo.monitor\tPipeWire\ts32le 2ch 48000Hz\tSUSPENDED\n"
+                        "another invalid line\n")))
+    (cl-letf (((symbol-function 'shell-command-to-string)
+               (lambda (_cmd) output)))
+      (let ((result (cj/recording-detect-system-device)))
+        (should (equal "alsa_output.pci-0000_00_1f.3.analog-stereo.monitor" result))))))
+
+(provide 'test-video-audio-recording-detect-system-device)
+;;; test-video-audio-recording-detect-system-device.el ends here