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+;;; test-music-config--art-valid-image.el --- Tests for fetched-image validation -*- coding: utf-8; lexical-binding: t; -*-
+;;
+;; Author: Craig Jennings <c@cjennings.net>
+;;
+;;; Commentary:
+;; Unit tests for `cj/music-art--valid-image-p': recognize whether fetched bytes
+;; are actually a displayable image, so an empty body, an HTML error page served
+;; 200, or a text response is rejected before it lands in the cache.  Detection
+;; is by image header (`image-type-from-data'), which works headless.
+;;
+;;; Code:
+
+(require 'ert)
+
+(defvar-keymap cj/custom-keymap :doc "Stub keymap for testing")
+
+(let ((emms-dir (car (file-expand-wildcards
+                      (expand-file-name "elpa/emms-*" user-emacs-directory)))))
+  (when emms-dir (add-to-list 'load-path emms-dir)))
+
+(require 'emms)
+(require 'music-config)
+
+(defconst test-art--png-1x1
+  (base64-decode-string
+   (concat "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk"
+           "YPhfDwAChwGA60e6kgAAAABJRU5ErkJggg=="))
+  "A minimal valid 1x1 PNG, as raw bytes.")
+
+(ert-deftest test-music-config--art-valid-image-normal-png ()
+  "Normal: real PNG bytes are recognized as a valid image."
+  (should (cj/music-art--valid-image-p test-art--png-1x1)))
+
+(ert-deftest test-music-config--art-valid-image-error-html ()
+  "Error: an HTML error page served 200 is not a valid image."
+  (should-not (cj/music-art--valid-image-p "<html><body>502 Bad Gateway</body></html>")))
+
+(ert-deftest test-music-config--art-valid-image-error-text ()
+  "Error: arbitrary text is not a valid image."
+  (should-not (cj/music-art--valid-image-p "this is not an image")))
+
+(ert-deftest test-music-config--art-valid-image-boundary-empty ()
+  "Boundary: an empty body is not a valid image."
+  (should-not (cj/music-art--valid-image-p "")))
+
+(ert-deftest test-music-config--art-valid-image-boundary-nil ()
+  "Boundary: nil is not a valid image."
+  (should-not (cj/music-art--valid-image-p nil)))
+
+(provide 'test-music-config--art-valid-image)
+;;; test-music-config--art-valid-image.el ends here