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+;;; test-wttrin--fetch-url.el --- Tests for wttrin--fetch-url -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024 Craig Jennings
+
+;;; Commentary:
+;; Unit tests for wttrin--fetch-url function.
+;; Tests the common async URL fetching logic extracted during refactoring.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin--fetch-url-normal-success-calls-callback-with-data ()
+  "Test that successful fetch calls callback with decoded data."
+  (let ((callback-called nil)
+        (callback-data nil))
+    ;; Mock url-retrieve to simulate successful response
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 ;; Simulate successful HTTP response
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n")
+                   (insert "Content-Type: text/plain\r\n")
+                   (insert "\r\n")
+                   (insert "Weather data here")
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-called t)
+         (setq callback-data data)))
+
+      ;; Verify callback was called with correct data
+      (should callback-called)
+      (should (string= "Weather data here" callback-data)))))
+
+(ert-deftest test-wttrin--fetch-url-normal-utf8-decoding ()
+  "Test that UTF-8 content is properly decoded."
+  (let ((callback-data nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n\r\n")
+                   (insert "Weather: ☀️ Sunny 中文")
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-data data)))
+
+      (should (string-match-p "☀️" callback-data))
+      (should (string-match-p "中文" callback-data)))))
+
+(ert-deftest test-wttrin--fetch-url-normal-headers-stripped ()
+  "Test that HTTP headers are correctly stripped from response."
+  (let ((callback-data nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n")
+                   (insert "Content-Type: text/plain\r\n")
+                   (insert "Content-Length: 17\r\n")
+                   (insert "\r\n")
+                   (insert "Weather data here")
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-data data)))
+
+      ;; Headers should not be in the data
+      (should-not (string-match-p "HTTP/1.1" callback-data))
+      (should-not (string-match-p "Content-Type" callback-data))
+      (should (string= "Weather data here" callback-data)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin--fetch-url-boundary-empty-response ()
+  "Test handling of empty response body."
+  (let ((callback-data nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n\r\n")
+                   ;; Empty body
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-data data)))
+
+      (should (string= "" callback-data)))))
+
+(ert-deftest test-wttrin--fetch-url-boundary-large-response ()
+  "Test handling of large response body."
+  (let ((callback-data nil)
+        (large-body (make-string 10000 ?x)))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n\r\n")
+                   (insert large-body)
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-data data)))
+
+      (should (= 10000 (length callback-data))))))
+
+(ert-deftest test-wttrin--fetch-url-boundary-unix-line-endings ()
+  "Test handling of Unix-style line endings (LF only)."
+  (let ((callback-data nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\n")
+                   (insert "Content-Type: text/plain\n")
+                   (insert "\n")
+                   (insert "Weather data")
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-data data)))
+
+      (should (string= "Weather data" callback-data)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin--fetch-url-error-network-error-calls-callback-with-nil ()
+  "Test that network errors result in callback being called with nil."
+  (let ((callback-called nil)
+        (callback-data 'not-nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 ;; Simulate network error
+                 (with-temp-buffer
+                   (funcall callback '(:error (error "Network unreachable")))))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-called t)
+         (setq callback-data data)))
+
+      (should callback-called)
+      (should (null callback-data)))))
+
+(ert-deftest test-wttrin--fetch-url-error-processing-error-calls-callback-with-nil ()
+  "Test that processing errors result in callback being called with nil."
+  (let ((callback-called nil)
+        (callback-data 'not-nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   ;; Simulate a real error by having decode-coding-string fail
+                   ;; Make buffer-substring-no-properties return invalid data
+                   (cl-letf (((symbol-function 'decode-coding-string)
+                              (lambda (string coding-system)
+                                (error "Decoding error"))))
+                     (insert "HTTP/1.1 200 OK\r\n\r\ndata")
+                     (funcall callback nil))))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-called t)
+         (setq callback-data data)))
+
+      ;; Should still call callback even on error
+      (should callback-called)
+      ;; But data should be nil due to error
+      (should (null callback-data)))))
+
+(ert-deftest test-wttrin--fetch-url-error-buffer-killed-after-processing ()
+  "Test that response buffer is properly killed after processing."
+  (let ((buffers-before (buffer-list))
+        (callback-called nil))
+    (cl-letf (((symbol-function 'url-retrieve)
+               (lambda (url callback)
+                 (with-temp-buffer
+                   (insert "HTTP/1.1 200 OK\r\n\r\ndata")
+                   (funcall callback nil)))))
+
+      (wttrin--fetch-url
+       "http://example.com/weather"
+       (lambda (data)
+         (setq callback-called t)))
+
+      (should callback-called)
+      ;; Buffer list should be the same (no leaked buffers)
+      (should (= (length buffers-before) (length (buffer-list)))))))
+
+(provide 'test-wttrin--fetch-url)
+;;; test-wttrin--fetch-url.el ends here