5 files changed, 508 insertions, 0 deletions
diff --git a/tests/test-wttrin-geolocation--parse-ipapi.el b/tests/test-wttrin-geolocation--parse-ipapi.el
new file mode 100644
index 0000000..26d67bc
--- /dev/null
+++ b/tests/test-wttrin-geolocation--parse-ipapi.el
@@ -0,0 +1,83 @@
+;;; test-wttrin-geolocation--parse-ipapi.el --- Tests for ipapi.co response parser -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for `wttrin-geolocation--parse-ipapi'.  Pure function — no
+;; network, no async.  Covers normal, boundary, and error cases per the
+;; Normal/Boundary/Error discipline.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin-geolocation)
+
+;;; Setup and Teardown
+
+(defun test-wttrin-geolocation--parse-ipapi-setup ()
+  "Setup for ipapi parser tests."
+  nil)
+
+(defun test-wttrin-geolocation--parse-ipapi-teardown ()
+  "Teardown for ipapi parser tests."
+  nil)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-normal-full-response-returns-formatted-string ()
+  "A full ipapi.co response yields \"City, Region\"."
+  (let ((json "{\"ip\":\"1.2.3.4\",\"city\":\"Berkeley\",\"region\":\"California\",\"country_name\":\"United States\",\"latitude\":37.87,\"longitude\":-122.27}"))
+    (should (string= "Berkeley, California"
+                     (wttrin-geolocation--parse-ipapi json)))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-normal-unicode-preserved ()
+  "Unicode city and region names round-trip through the parser."
+  (let ((json "{\"city\":\"São Paulo\",\"region\":\"São Paulo\"}"))
+    (should (string= "São Paulo, São Paulo"
+                     (wttrin-geolocation--parse-ipapi json)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-boundary-extra-fields-ignored ()
+  "Unknown fields in the response do not affect the parsed result."
+  (let ((json "{\"city\":\"Paris\",\"region\":\"Ile-de-France\",\"currency\":\"EUR\",\"asn\":\"AS1234\"}"))
+    (should (string= "Paris, Ile-de-France"
+                     (wttrin-geolocation--parse-ipapi json)))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-boundary-multi-word-city-preserved ()
+  "Multi-word city names are preserved verbatim."
+  (let ((json "{\"city\":\"New Orleans\",\"region\":\"Louisiana\"}"))
+    (should (string= "New Orleans, Louisiana"
+                     (wttrin-geolocation--parse-ipapi json)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-nil-input-returns-nil ()
+  "A nil input string returns nil."
+  (should-not (wttrin-geolocation--parse-ipapi nil)))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-empty-string-returns-nil ()
+  "An empty input string returns nil."
+  (should-not (wttrin-geolocation--parse-ipapi "")))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-malformed-json-returns-nil ()
+  "Malformed JSON returns nil rather than signalling."
+  (should-not (wttrin-geolocation--parse-ipapi "{not valid json")))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-missing-city-returns-nil ()
+  "A response without a city field returns nil."
+  (let ((json "{\"region\":\"California\"}"))
+    (should-not (wttrin-geolocation--parse-ipapi json))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-missing-region-returns-nil ()
+  "A response without a region field returns nil."
+  (let ((json "{\"city\":\"Berkeley\"}"))
+    (should-not (wttrin-geolocation--parse-ipapi json))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipapi-error-api-error-flag-returns-nil ()
+  "An ipapi rate-limit / error response returns nil even if city/region are absent."
+  (let ((json "{\"error\":true,\"reason\":\"RateLimited\",\"message\":\"wait\"}"))
+    (should-not (wttrin-geolocation--parse-ipapi json))))
+
+(provide 'test-wttrin-geolocation--parse-ipapi)
+;;; test-wttrin-geolocation--parse-ipapi.el ends here
diff --git a/tests/test-wttrin-geolocation--parse-ipinfo.el b/tests/test-wttrin-geolocation--parse-ipinfo.el
new file mode 100644
index 0000000..4543e32
--- /dev/null
+++ b/tests/test-wttrin-geolocation--parse-ipinfo.el
@@ -0,0 +1,61 @@
+;;; test-wttrin-geolocation--parse-ipinfo.el --- Tests for ipinfo.io response parser -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for `wttrin-geolocation--parse-ipinfo'.  Pure function — no
+;; network, no async.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin-geolocation)
+
+;;; Setup and Teardown
+
+(defun test-wttrin-geolocation--parse-ipinfo-setup ()
+  "Setup for ipinfo parser tests."
+  nil)
+
+(defun test-wttrin-geolocation--parse-ipinfo-teardown ()
+  "Teardown for ipinfo parser tests."
+  nil)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-normal-full-response-returns-formatted-string ()
+  "A full ipinfo.io response yields \"City, Region\"."
+  (let ((json "{\"ip\":\"8.8.8.8\",\"city\":\"Mountain View\",\"region\":\"California\",\"country\":\"US\",\"loc\":\"37.3860,-122.0838\",\"org\":\"AS15169 Google LLC\",\"postal\":\"94035\",\"timezone\":\"America/Los_Angeles\"}"))
+    (should (string= "Mountain View, California"
+                     (wttrin-geolocation--parse-ipinfo json)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-boundary-minimal-fields-works ()
+  "A response with only city and region parses correctly."
+  (let ((json "{\"city\":\"Berlin\",\"region\":\"Berlin\"}"))
+    (should (string= "Berlin, Berlin"
+                     (wttrin-geolocation--parse-ipinfo json)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-error-nil-input-returns-nil ()
+  "A nil input string returns nil."
+  (should-not (wttrin-geolocation--parse-ipinfo nil)))
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-error-malformed-json-returns-nil ()
+  "Malformed JSON returns nil rather than signalling."
+  (should-not (wttrin-geolocation--parse-ipinfo "not json at all")))
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-error-missing-city-returns-nil ()
+  "A response without a city field returns nil."
+  (let ((json "{\"region\":\"California\",\"country\":\"US\"}"))
+    (should-not (wttrin-geolocation--parse-ipinfo json))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipinfo-error-missing-region-returns-nil ()
+  "A response without a region field returns nil."
+  (let ((json "{\"city\":\"Mountain View\",\"country\":\"US\"}"))
+    (should-not (wttrin-geolocation--parse-ipinfo json))))
+
+(provide 'test-wttrin-geolocation--parse-ipinfo)
+;;; test-wttrin-geolocation--parse-ipinfo.el ends here
diff --git a/tests/test-wttrin-geolocation--parse-ipwhois.el b/tests/test-wttrin-geolocation--parse-ipwhois.el
new file mode 100644
index 0000000..14c8119
--- /dev/null
+++ b/tests/test-wttrin-geolocation--parse-ipwhois.el
@@ -0,0 +1,63 @@
+;;; test-wttrin-geolocation--parse-ipwhois.el --- Tests for ipwho.is response parser -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for `wttrin-geolocation--parse-ipwhois'.  Pure function — no
+;; network, no async.  The ipwho.is response carries a `success' flag which
+;; is false on rate-limit / lookup failure even when the response is
+;; well-formed JSON.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin-geolocation)
+
+;;; Setup and Teardown
+
+(defun test-wttrin-geolocation--parse-ipwhois-setup ()
+  "Setup for ipwho.is parser tests."
+  nil)
+
+(defun test-wttrin-geolocation--parse-ipwhois-teardown ()
+  "Teardown for ipwho.is parser tests."
+  nil)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-normal-success-response-returns-formatted-string ()
+  "A successful ipwho.is response yields \"City, Region\"."
+  (let ((json "{\"ip\":\"8.8.8.8\",\"success\":true,\"type\":\"IPv4\",\"country\":\"United States\",\"country_code\":\"US\",\"region\":\"California\",\"region_code\":\"CA\",\"city\":\"Mountain View\",\"latitude\":37.386,\"longitude\":-122.0838}"))
+    (should (string= "Mountain View, California"
+                     (wttrin-geolocation--parse-ipwhois json)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-boundary-unicode-preserved ()
+  "Unicode city and region names round-trip through the parser."
+  (let ((json "{\"success\":true,\"city\":\"München\",\"region\":\"Bayern\"}"))
+    (should (string= "München, Bayern"
+                     (wttrin-geolocation--parse-ipwhois json)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-error-nil-input-returns-nil ()
+  "A nil input string returns nil."
+  (should-not (wttrin-geolocation--parse-ipwhois nil)))
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-error-success-false-returns-nil ()
+  "A response with `success: false' returns nil even if city/region are present."
+  (let ((json "{\"success\":false,\"message\":\"rate limit reached\",\"city\":\"Anywhere\",\"region\":\"Anywhere\"}"))
+    (should-not (wttrin-geolocation--parse-ipwhois json))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-error-missing-city-returns-nil ()
+  "A success response without a city field returns nil."
+  (let ((json "{\"success\":true,\"region\":\"California\"}"))
+    (should-not (wttrin-geolocation--parse-ipwhois json))))
+
+(ert-deftest test-wttrin-geolocation--parse-ipwhois-error-malformed-json-returns-nil ()
+  "Malformed JSON returns nil rather than signalling."
+  (should-not (wttrin-geolocation--parse-ipwhois "{\"success\":true,\"city\":")))
+
+(provide 'test-wttrin-geolocation--parse-ipwhois)
+;;; test-wttrin-geolocation--parse-ipwhois.el ends here
diff --git a/tests/test-wttrin-geolocation-detect.el b/tests/test-wttrin-geolocation-detect.el
new file mode 100644
index 0000000..ccd113f
--- /dev/null
+++ b/tests/test-wttrin-geolocation-detect.el
@@ -0,0 +1,179 @@
+;;; test-wttrin-geolocation-detect.el --- Tests for wttrin-geolocation-detect -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for `wttrin-geolocation-detect'.  Mocks `url-retrieve' at
+;; the boundary — exercises the real extract/parse logic via the selected
+;; provider.  No network, no async timing.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'wttrin-geolocation)
+
+;;; Setup and Teardown
+
+(defun test-wttrin-geolocation-detect-setup ()
+  "Setup for detect tests — pin provider to ipapi for determinism."
+  (setq wttrin-geolocation-provider 'ipapi))
+
+(defun test-wttrin-geolocation-detect-teardown ()
+  "Teardown for detect tests — restore default provider."
+  (setq wttrin-geolocation-provider 'ipapi))
+
+;;; Helpers
+
+(defmacro test-wttrin-geolocation-detect--with-http (status body-string &rest body)
+  "Run BODY with `url-retrieve' mocked to return HTTP STATUS and BODY-STRING.
+The mock writes a full HTTP response into a temp buffer and invokes the
+retrieval callback with a nil status plist (success)."
+  (declare (indent 2))
+  `(cl-letf (((symbol-function 'url-retrieve)
+              (lambda (_url callback)
+                (with-temp-buffer
+                  (insert (format "HTTP/1.1 %d OK\r\n" ,status))
+                  (insert "Content-Type: application/json\r\n\r\n")
+                  (insert ,body-string)
+                  (funcall callback nil)))))
+     ,@body))
+
+(defmacro test-wttrin-geolocation-detect--with-network-error (&rest body)
+  "Run BODY with `url-retrieve' mocked to report a network-level error."
+  (declare (indent 0))
+  `(cl-letf (((symbol-function 'url-retrieve)
+              (lambda (_url callback)
+                (with-temp-buffer
+                  (funcall callback '(:error (error "Network unreachable")))))))
+     ,@body))
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation-detect-normal-ipapi-success-callback-receives-location ()
+  "A successful ipapi response leads to the callback receiving \"City, Region\"."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 200
+            "{\"city\":\"Berkeley\",\"region\":\"California\"}"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should (string= "Berkeley, California" result)))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-normal-selected-provider-used ()
+  "Switching `wttrin-geolocation-provider' routes through that provider's URL and parser."
+  (let ((wttrin-geolocation-provider 'ipinfo)
+        (requested-url nil)
+        (result nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (setq requested-url url)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n\r\n")
+                   (insert "{\"city\":\"Mountain View\",\"region\":\"California\",\"loc\":\"37.4,-122.0\"}")
+                   (funcall callback nil)))))
+      (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+    (should (string= "https://ipinfo.io/json" requested-url))
+    (should (string= "Mountain View, California" result))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation-detect-boundary-parser-returns-nil-callback-gets-nil ()
+  "If the parser rejects the response (missing fields), the callback receives nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 200
+            "{\"city\":\"Berkeley\"}"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-boundary-ipapi-rate-limit-error-flag-returns-nil ()
+  "An ipapi rate-limit response (HTTP 200 with error flag) yields nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 200
+            "{\"error\":true,\"reason\":\"RateLimited\"}"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation-detect-error-network-failure-calls-callback-with-nil ()
+  "A network-level error surfaces as nil to the callback."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((called nil)
+            (result 'unset))
+        (test-wttrin-geolocation-detect--with-network-error
+          (wttrin-geolocation-detect (lambda (loc)
+                                       (setq called t)
+                                       (setq result loc))))
+        (should called)
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-http-429-returns-nil ()
+  "An HTTP 429 rate-limit response yields nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 429
+            "{\"error\":\"rate limit\"}"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-http-500-returns-nil ()
+  "An HTTP 500 server error yields nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 500
+            "Internal Server Error"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-empty-body-returns-nil ()
+  "An empty response body yields nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 200 ""
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-malformed-json-returns-nil ()
+  "Malformed JSON in the response body yields nil."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((result 'unset))
+        (test-wttrin-geolocation-detect--with-http 200 "{not valid json"
+          (wttrin-geolocation-detect (lambda (loc) (setq result loc))))
+        (should-not result))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-buffer-cleanup-after-success ()
+  "The response buffer is killed after a successful fetch (no leaks)."
+  (test-wttrin-geolocation-detect-setup)
+  (unwind-protect
+      (let ((buffers-before (length (buffer-list))))
+        (test-wttrin-geolocation-detect--with-http 200
+            "{\"city\":\"Paris\",\"region\":\"IDF\"}"
+          (wttrin-geolocation-detect #'ignore))
+        (should (= buffers-before (length (buffer-list)))))
+    (test-wttrin-geolocation-detect-teardown)))
+
+(ert-deftest test-wttrin-geolocation-detect-error-unknown-provider-signals-error ()
+  "Selecting an unknown provider signals a clear error."
+  (let ((wttrin-geolocation-provider 'nonexistent-provider))
+    (should-error (wttrin-geolocation-detect #'ignore) :type 'error)))
+
+(provide 'test-wttrin-geolocation-detect)
+;;; test-wttrin-geolocation-detect.el ends here
diff --git a/tests/test-wttrin-set-location-from-geolocation.el b/tests/test-wttrin-set-location-from-geolocation.el
new file mode 100644
index 0000000..170d0fb
--- /dev/null
+++ b/tests/test-wttrin-set-location-from-geolocation.el
@@ -0,0 +1,122 @@
+;;; test-wttrin-set-location-from-geolocation.el --- Tests for wttrin-set-location-from-geolocation -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for the interactive `wttrin-set-location-from-geolocation'
+;; command.  Mocks `wttrin-geolocation-detect' (to invoke the callback
+;; synchronously with a chosen value) and `yes-or-no-p' (to simulate
+;; user consent).  Does not hit the network and does not prompt.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'wttrin)
+(require 'wttrin-geolocation)
+
+;;; Setup and Teardown
+
+(defvar test-wttrin-set-location-from-geolocation--saved-favorite nil
+  "Snapshot of `wttrin-favorite-location' restored in teardown.")
+
+(defun test-wttrin-set-location-from-geolocation-setup ()
+  "Snapshot `wttrin-favorite-location' and clear it for the test."
+  (setq test-wttrin-set-location-from-geolocation--saved-favorite
+        wttrin-favorite-location)
+  (setq wttrin-favorite-location nil))
+
+(defun test-wttrin-set-location-from-geolocation-teardown ()
+  "Restore `wttrin-favorite-location' to its pre-test value."
+  (setq wttrin-favorite-location
+        test-wttrin-set-location-from-geolocation--saved-favorite))
+
+;;; Helpers
+
+(defmacro test-wttrin-set-location--with-detected (location confirm &rest body)
+  "Run BODY with `wttrin-geolocation-detect' returning LOCATION and `yes-or-no-p' returning CONFIRM."
+  (declare (indent 2))
+  `(cl-letf (((symbol-function 'wttrin-geolocation-detect)
+              (lambda (callback) (funcall callback ,location)))
+             ((symbol-function 'yes-or-no-p)
+              (lambda (&rest _) ,confirm)))
+     ,@body))
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-set-location-from-geolocation-normal-confirm-sets-variable ()
+  "Successful detection followed by user confirmation sets the favorite."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (unwind-protect
+      (progn
+        (test-wttrin-set-location--with-detected "Berkeley, California" t
+          (wttrin-set-location-from-geolocation))
+        (should (string= "Berkeley, California" wttrin-favorite-location)))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+(ert-deftest test-wttrin-set-location-from-geolocation-normal-decline-leaves-variable-unchanged ()
+  "Successful detection followed by user declining leaves the favorite untouched."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (setq wttrin-favorite-location "Pre-existing, Place")
+  (unwind-protect
+      (progn
+        (test-wttrin-set-location--with-detected "Berkeley, California" nil
+          (wttrin-set-location-from-geolocation))
+        (should (string= "Pre-existing, Place" wttrin-favorite-location)))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-set-location-from-geolocation-boundary-unicode-location ()
+  "A Unicode location string round-trips into the favorite variable."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (unwind-protect
+      (progn
+        (test-wttrin-set-location--with-detected "München, Bayern" t
+          (wttrin-set-location-from-geolocation))
+        (should (string= "München, Bayern" wttrin-favorite-location)))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-set-location-from-geolocation-error-nil-detection-leaves-variable-unchanged ()
+  "When detection returns nil, the favorite variable is not modified."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (setq wttrin-favorite-location "Pre-existing, Place")
+  (unwind-protect
+      (progn
+        (test-wttrin-set-location--with-detected nil t
+          (wttrin-set-location-from-geolocation))
+        (should (string= "Pre-existing, Place" wttrin-favorite-location)))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+(ert-deftest test-wttrin-set-location-from-geolocation-error-nil-detection-does-not-prompt ()
+  "When detection returns nil, the user is not prompted for confirmation."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (unwind-protect
+      (let ((prompt-called nil))
+        (cl-letf (((symbol-function 'wttrin-geolocation-detect)
+                   (lambda (callback) (funcall callback nil)))
+                  ((symbol-function 'yes-or-no-p)
+                   (lambda (&rest _) (setq prompt-called t) t)))
+          (wttrin-set-location-from-geolocation))
+        (should-not prompt-called))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+(ert-deftest test-wttrin-set-location-from-geolocation-error-detection-failure-shows-message ()
+  "When detection returns nil, the user sees a diagnostic message."
+  (test-wttrin-set-location-from-geolocation-setup)
+  (unwind-protect
+      (let ((messages nil))
+        (cl-letf (((symbol-function 'wttrin-geolocation-detect)
+                   (lambda (callback) (funcall callback nil)))
+                  ((symbol-function 'message)
+                   (lambda (fmt &rest args)
+                     (push (apply #'format fmt args) messages))))
+          (wttrin-set-location-from-geolocation))
+        (should (cl-some (lambda (m) (string-match-p "[Cc]ould not detect" m))
+                         messages)))
+    (test-wttrin-set-location-from-geolocation-teardown)))
+
+(provide 'test-wttrin-set-location-from-geolocation)
+;;; test-wttrin-set-location-from-geolocation.el ends here