test(host-environment): cover laptop/desktop, platform, display, timezone predicates

Four new test files extending the existing test-host-environment.el
(which already covered the two battery helpers).

- platform-predicates: env-linux-p, env-bsd-p, env-macos-p, env-windows-p
  walked across every supported system-type value. 8 tests.
- display-predicates: env-x-p, env-x11-p, env-wayland-p, env-terminal-p,
  env-gui-p exercised under every relevant combination of window-system,
  WAYLAND_DISPLAY, and display-graphic-p. 13 tests.
- env-laptop-p: composition over the helpers, with Linux dispatch
  isolated from non-Linux dispatch via system-type binding. 8 tests
  including env-desktop-p as the inverse. battery-status-function is
  forward-declared in this test file (initialized to nil) so cl-letf's
  symbol-value place can read the prior value without hitting
  void-variable.
- detect-system-timezone: the four-method priority chain. Mocks
  cj/match-localtime-to-zoneinfo and getenv at the boundary; uses
  cl-letf on file-exists-p / insert-file-contents to exercise the
  /etc/timezone fall-through without touching real system files.
  5 tests.

34 new tests for host-environment, all passing. Full suite green.

1 files changed, 92 insertions, 0 deletions

diff --git a/tests/test-host-environment--env-laptop-p.el b/tests/test-host-environment--env-laptop-p.el
new file mode 100644
index 00000000..da00954c
--- /dev/null
+++ b/tests/test-host-environment--env-laptop-p.el
@@ -0,0 +1,92 @@
+;;; test-host-environment--env-laptop-p.el --- Tests for env-laptop-p / env-desktop-p -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `env-laptop-p' and the inverse `env-desktop-p'.  On Linux,
+;; the function delegates to `env--power-supply-has-battery-p' against
+;; /sys/class/power_supply.  On other platforms, it reads the battery
+;; status char.  Tests mock `system-type' and the helpers at their
+;; boundary so the predicate's dispatch logic is exercised without
+;; touching real system files.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'host-environment)
+
+;; Forward-declare and initialize to nil so let-binding inside tests
+;; sees this as special under lexical-binding, and so cl-letf's
+;; symbol-value place can read the old value without hitting void-variable.
+(defvar battery-status-function nil)
+
+;;; env-laptop-p — Linux dispatch
+
+(ert-deftest test-host-environment-laptop-p-linux-with-battery ()
+  "Normal: on Linux, env-laptop-p delegates to power-supply helper."
+  (let ((system-type 'gnu/linux))
+    (cl-letf (((symbol-function 'env--power-supply-has-battery-p)
+               (lambda (_dir) t)))
+      (should (env-laptop-p)))))
+
+(ert-deftest test-host-environment-laptop-p-linux-without-battery ()
+  "Boundary: on Linux, env-laptop-p returns nil when no BAT* dir is found."
+  (let ((system-type 'gnu/linux))
+    (cl-letf (((symbol-function 'env--power-supply-has-battery-p)
+               (lambda (_dir) nil)))
+      (should-not (env-laptop-p)))))
+
+(ert-deftest test-host-environment-laptop-p-linux-passes-correct-dir ()
+  "Boundary: on Linux, the power-supply helper receives /sys/class/power_supply."
+  (let ((system-type 'gnu/linux)
+        captured)
+    (cl-letf (((symbol-function 'env--power-supply-has-battery-p)
+               (lambda (dir) (setq captured dir) t)))
+      (env-laptop-p)
+      (should (equal captured "/sys/class/power_supply")))))
+
+;;; env-laptop-p — non-Linux dispatch via battery-format
+
+(ert-deftest test-host-environment-laptop-p-non-linux-with-battery-char ()
+  "Normal: on non-Linux, env-laptop-p reads the battery status char."
+  (let ((system-type 'darwin))
+    (cl-letf (((symbol-function 'require)
+               (lambda (feat &rest _) (eq feat 'battery)))
+              ((symbol-function 'battery-format)
+               (lambda (_format _data) "+"))
+              ((symbol-value 'battery-status-function) (lambda () 'fake-data)))
+      (should (env-laptop-p)))))
+
+(ert-deftest test-host-environment-laptop-p-non-linux-no-battery-char ()
+  "Boundary: on non-Linux, an N/A char means no battery."
+  (let ((system-type 'darwin))
+    (cl-letf (((symbol-function 'require)
+               (lambda (feat &rest _) (eq feat 'battery)))
+              ((symbol-function 'battery-format)
+               (lambda (_format _data) "N/A"))
+              ((symbol-value 'battery-status-function) (lambda () 'fake-data)))
+      (should-not (env-laptop-p)))))
+
+(ert-deftest test-host-environment-laptop-p-non-linux-no-battery-feature ()
+  "Error: on non-Linux without the battery feature, env-laptop-p returns nil."
+  (let ((system-type 'darwin))
+    (cl-letf (((symbol-function 'require)
+               (lambda (_feat &rest _) nil))
+              ((symbol-value 'battery-status-function) nil))
+      (should-not (env-laptop-p)))))
+
+;;; env-desktop-p — inverse of env-laptop-p
+
+(ert-deftest test-host-environment-desktop-p-true-when-not-laptop ()
+  "Normal: env-desktop-p is t when env-laptop-p is nil."
+  (cl-letf (((symbol-function 'env-laptop-p) (lambda () nil)))
+    (should (env-desktop-p))))
+
+(ert-deftest test-host-environment-desktop-p-nil-when-laptop ()
+  "Boundary: env-desktop-p is nil when env-laptop-p is non-nil."
+  (cl-letf (((symbol-function 'env-laptop-p) (lambda () t)))
+    (should-not (env-desktop-p))))
+
+(provide 'test-host-environment--env-laptop-p)
+;;; test-host-environment--env-laptop-p.el ends here