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+;;; test-wttrin-favorite-override.el --- Tests for the runtime favorite override -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for the split between the configured favorite
+;; (`wttrin-favorite-location', a defcustom set in init) and the runtime
+;; favorite (`wttrin--favorite-override', set by `d'/the geolocation commands
+;; and persisted by savehist).  The effective favorite resolves via
+;; `wttrin--favorite-location': the override wins over the config, so a favorite
+;; chosen at runtime is not clobbered by an init that also sets the option.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'wttrin)
+
+;;; wttrin--favorite-location (resolver)
+
+(ert-deftest test-wttrin-favorite-override-normal-config-when-no-override ()
+  "Normal: with no override, the effective favorite is the configured one."
+  (let ((wttrin-favorite-location "New Orleans, LA")
+        (wttrin--favorite-override nil))
+    (should (equal "New Orleans, LA" (wttrin--favorite-location)))))
+
+(ert-deftest test-wttrin-favorite-override-normal-override-wins ()
+  "Normal: a runtime override shadows the configured favorite."
+  (let ((wttrin-favorite-location "New Orleans, LA")
+        (wttrin--favorite-override "Hyatt Place Warwick, RI"))
+    (should (equal "Hyatt Place Warwick, RI" (wttrin--favorite-location)))))
+
+(ert-deftest test-wttrin-favorite-override-boundary-both-nil ()
+  "Boundary: no config and no override yields nil (favorite disabled)."
+  (let ((wttrin-favorite-location nil)
+        (wttrin--favorite-override nil))
+    (should (null (wttrin--favorite-location)))))
+
+(ert-deftest test-wttrin-favorite-override-boundary-auto-detect-override ()
+  "Boundary: the override carries the tri-state t (auto-detect)."
+  (let ((wttrin-favorite-location "New Orleans, LA")
+        (wttrin--favorite-override t))
+    (should (eq t (wttrin--favorite-location)))))
+
+(ert-deftest test-wttrin-favorite-override-regression-init-does-not-clobber ()
+  "Regression: setting the config after an override (as an init `setopt' would)
+does not change the effective favorite.  This is the bug where a favorite set
+with `d' reverted to the init value on restart."
+  (let ((wttrin--favorite-override "Hyatt Place Warwick, RI")
+        (wttrin-favorite-location nil))
+    ;; Simulate the init running its (setopt wttrin-favorite-location ...).
+    (setq wttrin-favorite-location "New Orleans, LA")
+    (should (equal "Hyatt Place Warwick, RI" (wttrin--favorite-location)))))
+
+;;; wttrin--set-favorite-location writes the override, not the config
+
+(ert-deftest test-wttrin-favorite-override-normal-setter-writes-override ()
+  "Normal: the setter writes the runtime override and leaves the config intact."
+  (let ((wttrin-favorite-location "New Orleans, LA")
+        (wttrin--favorite-override nil)
+        (wttrin--location-history nil))
+    (wttrin--set-favorite-location "Paris, FR")
+    (should (equal "Paris, FR" wttrin--favorite-override))
+    (should (equal "New Orleans, LA" wttrin-favorite-location))
+    (should (equal "Paris, FR" (wttrin--favorite-location)))))
+
+;;; savehist registration covers only the scrub-tolerant search history;
+;;; the runtime vars persist in `wttrin-state-file' (see test-wttrin-state-file.el)
+
+(ert-deftest test-wttrin-favorite-override-normal-savehist-excludes-runtime-vars ()
+  "Normal: savehist persists neither the runtime vars nor the config defcustoms.
+The runtime favorite and directory live in `wttrin-state-file' — a savehist
+entry would be scrubbed by any session that saves savehist without wttrin."
+  (require 'savehist)
+  (let ((savehist-additional-variables '(kill-ring)))
+    (wttrin--savehist-register)
+    (should-not (memq 'wttrin--favorite-override savehist-additional-variables))
+    (should-not (memq 'wttrin--saved-locations-runtime savehist-additional-variables))
+    (should-not (memq 'wttrin-favorite-location savehist-additional-variables))
+    (should-not (memq 'wttrin-saved-locations savehist-additional-variables))))
+
+(provide 'test-wttrin-favorite-override)
+;;; test-wttrin-favorite-override.el ends here