test: cover wttrin-geolocation internal helpers

Four pure helpers in wttrin-geolocation.el were exercised only indirectly through the parser tests: --decode-json, --format-city-region, --lookup-provider, and --extract-body. None of them had direct unit coverage. Edge cases like an empty JSON object, a missing-vs-empty city field, an unknown provider symbol, or a missing HTTP body separator weren't locked.

The new file groups all four functions together. Each gets Normal, Boundary, and Error cases per testing.md. Highlights:

- --decode-json: distinguishes nil input, empty string, and malformed JSON, all of which return nil for different reasons.
- --format-city-region: separates "missing key" from "empty string" since the predicate `(and (stringp city) (> (length city) 0) ...)` short-circuits on either.
- --lookup-provider: tests two of the three built-ins plus a `let`-bound synthetic provider, locking the documented extension point on `wttrin-geolocation--providers`.
- --extract-body: real UTF-8 bytes inserted into a temp buffer (mirroring what `url-retrieve` delivers) verify the decoding path. 4xx, 5xx, and missing-separator paths each get their own test.

21 new tests, all green on first run since they characterize existing behavior.

1 files changed, 187 insertions, 0 deletions

diff --git a/tests/test-wttrin-geolocation--internals.el b/tests/test-wttrin-geolocation--internals.el
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+;;; test-wttrin-geolocation--internals.el --- Tests for geolocation internal helpers -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+
+;; Unit tests for the four pure helpers used by the geolocation parsers:
+;;   - wttrin-geolocation--decode-json
+;;   - wttrin-geolocation--format-city-region
+;;   - wttrin-geolocation--lookup-provider
+;;   - wttrin-geolocation--extract-body
+;;
+;; These functions are exercised indirectly through the parser tests
+;; (test-wttrin-geolocation--parse-ipapi.el and friends), but were not
+;; covered directly.  This file fills the gap so each helper's edge
+;; cases are locked in isolation.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin-geolocation)
+
+;;; --------------------------------------------------------------------------
+;;; wttrin-geolocation--decode-json
+;;; --------------------------------------------------------------------------
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--decode-json-normal-valid-object ()
+  "Valid JSON object decodes to an alist with symbol keys."
+  (let ((result (wttrin-geolocation--decode-json "{\"city\":\"Paris\",\"region\":\"IDF\"}")))
+    (should (equal (cdr (assq 'city result)) "Paris"))
+    (should (equal (cdr (assq 'region result)) "IDF"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--decode-json-boundary-empty-object ()
+  "Empty JSON object decodes to nil (an empty alist)."
+  (should (equal (wttrin-geolocation--decode-json "{}") nil)))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--decode-json-error-nil-input ()
+  "Nil input returns nil with no signal."
+  (should-not (wttrin-geolocation--decode-json nil)))
+
+(ert-deftest test-wttrin-geolocation--decode-json-error-empty-string ()
+  "Empty string returns nil with no signal."
+  (should-not (wttrin-geolocation--decode-json "")))
+
+(ert-deftest test-wttrin-geolocation--decode-json-error-malformed-json ()
+  "Malformed JSON returns nil with no signal."
+  (should-not (wttrin-geolocation--decode-json "not valid json {")))
+
+;;; --------------------------------------------------------------------------
+;;; wttrin-geolocation--format-city-region
+;;; --------------------------------------------------------------------------
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--format-city-region-normal-both-present ()
+  "City and region both present produces \"City, Region\"."
+  (let ((data '((city . "Paris") (region . "Île-de-France"))))
+    (should (equal (wttrin-geolocation--format-city-region data)
+                   "Paris, Île-de-France"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--format-city-region-boundary-empty-city ()
+  "Empty city string returns nil even when region is present."
+  (let ((data '((city . "") (region . "Île-de-France"))))
+    (should-not (wttrin-geolocation--format-city-region data))))
+
+(ert-deftest test-wttrin-geolocation--format-city-region-boundary-empty-region ()
+  "Empty region string returns nil even when city is present."
+  (let ((data '((city . "Paris") (region . ""))))
+    (should-not (wttrin-geolocation--format-city-region data))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--format-city-region-error-missing-city-key ()
+  "Missing city key returns nil."
+  (let ((data '((region . "Île-de-France"))))
+    (should-not (wttrin-geolocation--format-city-region data))))
+
+(ert-deftest test-wttrin-geolocation--format-city-region-error-missing-region-key ()
+  "Missing region key returns nil."
+  (let ((data '((city . "Paris"))))
+    (should-not (wttrin-geolocation--format-city-region data))))
+
+(ert-deftest test-wttrin-geolocation--format-city-region-error-nil-data ()
+  "Nil data returns nil with no signal."
+  (should-not (wttrin-geolocation--format-city-region nil)))
+
+;;; --------------------------------------------------------------------------
+;;; wttrin-geolocation--lookup-provider
+;;; --------------------------------------------------------------------------
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--lookup-provider-normal-builtin-ipapi ()
+  "Built-in ipapi provider returns its plist with :name, :url, :parser."
+  (let ((result (wttrin-geolocation--lookup-provider 'ipapi)))
+    (should (equal (plist-get result :name) "ipapi.co"))
+    (should (stringp (plist-get result :url)))
+    (should (eq (plist-get result :parser) 'wttrin-geolocation--parse-ipapi))))
+
+(ert-deftest test-wttrin-geolocation--lookup-provider-normal-builtin-ipinfo ()
+  "Built-in ipinfo provider returns its plist."
+  (let ((result (wttrin-geolocation--lookup-provider 'ipinfo)))
+    (should (equal (plist-get result :name) "ipinfo.io"))
+    (should (eq (plist-get result :parser) 'wttrin-geolocation--parse-ipinfo))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--lookup-provider-boundary-custom-registered ()
+  "User-registered provider is reachable via lookup."
+  (let ((wttrin-geolocation--providers
+         (cons '(test-provider
+                 :name "Test"
+                 :url "https://example.invalid/"
+                 :parser ignore)
+               wttrin-geolocation--providers)))
+    (let ((result (wttrin-geolocation--lookup-provider 'test-provider)))
+      (should (equal (plist-get result :name) "Test"))
+      (should (eq (plist-get result :parser) 'ignore)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--lookup-provider-error-unknown-symbol ()
+  "Unknown provider symbol signals error."
+  (should-error (wttrin-geolocation--lookup-provider 'definitely-not-registered)
+                :type 'error))
+
+;;; --------------------------------------------------------------------------
+;;; wttrin-geolocation--extract-body
+;;; --------------------------------------------------------------------------
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-geolocation--extract-body-normal-200-with-body ()
+  "200 OK response with CRLF separator returns the body."
+  (with-temp-buffer
+    (insert "HTTP/1.1 200 OK\r\nContent-Type: application/json\r\n\r\n{\"city\":\"Paris\"}")
+    (should (equal (wttrin-geolocation--extract-body)
+                   "{\"city\":\"Paris\"}"))))
+
+(ert-deftest test-wttrin-geolocation--extract-body-normal-utf8-body ()
+  "UTF-8 body bytes are decoded correctly."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (insert "HTTP/1.1 200 OK\r\n\r\n")
+    (insert (encode-coding-string "{\"city\":\"São Paulo\"}" 'utf-8))
+    (set-buffer-multibyte t)
+    (should (equal (wttrin-geolocation--extract-body)
+                   "{\"city\":\"São Paulo\"}"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-geolocation--extract-body-boundary-empty-body ()
+  "200 response with empty body returns the empty string."
+  (with-temp-buffer
+    (insert "HTTP/1.1 200 OK\r\n\r\n")
+    (should (equal (wttrin-geolocation--extract-body) ""))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-geolocation--extract-body-error-404 ()
+  "404 response returns nil."
+  (with-temp-buffer
+    (insert "HTTP/1.1 404 Not Found\r\n\r\nNot Found")
+    (should-not (wttrin-geolocation--extract-body))))
+
+(ert-deftest test-wttrin-geolocation--extract-body-error-500 ()
+  "500 response returns nil."
+  (with-temp-buffer
+    (insert "HTTP/1.1 500 Internal Server Error\r\n\r\noops")
+    (should-not (wttrin-geolocation--extract-body))))
+
+(ert-deftest test-wttrin-geolocation--extract-body-error-missing-separator ()
+  "Response without a blank-line separator returns nil."
+  (with-temp-buffer
+    (insert "HTTP/1.1 200 OK\r\nContent-Type: application/json\r\nbody-without-separator")
+    (should-not (wttrin-geolocation--extract-body))))
+
+(provide 'test-wttrin-geolocation--internals)
+;;; test-wttrin-geolocation--internals.el ends here