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, 63 insertions, 0 deletions

diff --git a/tests/test-host-environment--platform-predicates.el b/tests/test-host-environment--platform-predicates.el
new file mode 100644
index 00000000..3430a939
--- /dev/null
+++ b/tests/test-host-environment--platform-predicates.el
@@ -0,0 +1,63 @@
+;;; test-host-environment--platform-predicates.el --- Tests for env-linux/bsd/macos/windows-p -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the platform predicates in host-environment.el.  Each is a
+;; thin wrapper around `system-type'.  Tests rely on `system-type'
+;; being a special variable (so a `let'-binding shadows the global
+;; value) and walk every supported platform to confirm the right
+;; predicate returns t.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'host-environment)
+
+(ert-deftest test-host-environment-linux-p-true-on-gnu-linux ()
+  "Normal: env-linux-p returns t when system-type is gnu/linux."
+  (let ((system-type 'gnu/linux))
+    (should (env-linux-p))))
+
+(ert-deftest test-host-environment-linux-p-false-on-other-platforms ()
+  "Boundary: env-linux-p returns nil on every non-Linux platform."
+  (dolist (other '(darwin berkeley-unix windows-nt cygwin ms-dos))
+    (let ((system-type other))
+      (should-not (env-linux-p)))))
+
+(ert-deftest test-host-environment-bsd-p-true-on-berkeley-unix ()
+  "Normal: env-bsd-p returns t when system-type is berkeley-unix."
+  (let ((system-type 'berkeley-unix))
+    (should (env-bsd-p))))
+
+(ert-deftest test-host-environment-bsd-p-false-on-other-platforms ()
+  "Boundary: env-bsd-p returns nil on every non-BSD platform."
+  (dolist (other '(gnu/linux darwin windows-nt cygwin ms-dos))
+    (let ((system-type other))
+      (should-not (env-bsd-p)))))
+
+(ert-deftest test-host-environment-macos-p-true-on-darwin ()
+  "Normal: env-macos-p returns t when system-type is darwin."
+  (let ((system-type 'darwin))
+    (should (env-macos-p))))
+
+(ert-deftest test-host-environment-macos-p-false-on-other-platforms ()
+  "Boundary: env-macos-p returns nil on every non-Darwin platform."
+  (dolist (other '(gnu/linux berkeley-unix windows-nt cygwin ms-dos))
+    (let ((system-type other))
+      (should-not (env-macos-p)))))
+
+(ert-deftest test-host-environment-windows-p-true-on-each-windows-variant ()
+  "Normal: env-windows-p returns t on cygwin, windows-nt, and ms-dos."
+  (dolist (win '(cygwin windows-nt ms-dos))
+    (let ((system-type win))
+      (should (env-windows-p)))))
+
+(ert-deftest test-host-environment-windows-p-false-on-unix-platforms ()
+  "Boundary: env-windows-p returns nil on Unix-family platforms."
+  (dolist (other '(gnu/linux darwin berkeley-unix))
+    (let ((system-type other))
+      (should-not (env-windows-p)))))
+
+(provide 'test-host-environment--platform-predicates)
+;;; test-host-environment--platform-predicates.el ends here