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+;;; test-ai-config-current-model-selection.el --- Tests for cj/gptel--current-model-selection -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for cj/gptel--current-model-selection from ai-config.el.
+;;
+;; Pure function that formats the active backend and model into a display
+;; string like "Anthropic - Claude: claude-opus-4-6".  Used as the default
+;; selection in the model-switching completing-read prompt.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'testutil-ai-config)
+(require 'ai-config)
+
+;;; Normal Cases
+
+(ert-deftest test-ai-config-current-model-selection-normal-matching-backend ()
+  "When current backend is in the backends alist, use its display name."
+  (let* ((backend-obj 'my-backend)
+         (backends `(("Anthropic - Claude" . ,backend-obj))))
+    (should (equal (cj/gptel--current-model-selection backends backend-obj "opus")
+                   "Anthropic - Claude: opus"))))
+
+(ert-deftest test-ai-config-current-model-selection-normal-symbol-model ()
+  "Symbol model should be converted to string in the output."
+  (let* ((backend-obj 'my-backend)
+         (backends `(("Claude" . ,backend-obj))))
+    (should (equal (cj/gptel--current-model-selection backends backend-obj 'opus)
+                   "Claude: opus"))))
+
+(ert-deftest test-ai-config-current-model-selection-normal-multiple-backends ()
+  "Should find the correct backend name among multiple backends."
+  (let* ((backend-a 'backend-a)
+         (backend-b 'backend-b)
+         (backends `(("Claude" . ,backend-a) ("OpenAI" . ,backend-b))))
+    (should (equal (cj/gptel--current-model-selection backends backend-b "gpt-4o")
+                   "OpenAI: gpt-4o"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-ai-config-current-model-selection-boundary-nil-backend-shows-ai ()
+  "Nil backend (not in alist) should fall back to \"AI\"."
+  (should (equal (cj/gptel--current-model-selection '(("Claude" . x)) nil "opus")
+                 "AI: opus")))
+
+(ert-deftest test-ai-config-current-model-selection-boundary-unknown-backend-shows-ai ()
+  "Backend not found in alist should fall back to \"AI\"."
+  (should (equal (cj/gptel--current-model-selection
+                  '(("Claude" . backend-a)) 'unknown-backend "opus")
+                 "AI: opus")))
+
+(ert-deftest test-ai-config-current-model-selection-boundary-nil-model ()
+  "Nil model should produce \"nil\" in the model position (symbolp nil)."
+  (let* ((backend 'my-backend)
+         (backends `(("Claude" . ,backend))))
+    (should (equal (cj/gptel--current-model-selection backends backend nil)
+                   "Claude: nil"))))
+
+(ert-deftest test-ai-config-current-model-selection-boundary-empty-backends ()
+  "Empty backends alist should fall back to \"AI\" for backend name."
+  (should (equal (cj/gptel--current-model-selection nil 'anything "model")
+                 "AI: model")))
+
+(ert-deftest test-ai-config-current-model-selection-boundary-both-nil ()
+  "Nil backend and nil model should produce \"AI: nil\"."
+  (should (equal (cj/gptel--current-model-selection nil nil nil)
+                 "AI: nil")))
+
+(provide 'test-ai-config-current-model-selection)
+;;; test-ai-config-current-model-selection.el ends here