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+;;; test-ai-config-model-to-string.el --- Tests for cj/gptel--model-to-string -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for cj/gptel--model-to-string from ai-config.el.
+;;
+;; Pure function that converts a model identifier (string, symbol, or
+;; other type) to a string representation.  Branches on input type:
+;; string (identity), symbol (symbol-name), fallback (format).
+
+;;; 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-model-to-string-normal-string-returns-string ()
+  "String model name should be returned unchanged."
+  (should (equal (cj/gptel--model-to-string "claude-opus-4-6") "claude-opus-4-6")))
+
+(ert-deftest test-ai-config-model-to-string-normal-symbol-returns-symbol-name ()
+  "Symbol model name should return its symbol-name."
+  (should (equal (cj/gptel--model-to-string 'gpt-4o) "gpt-4o")))
+
+(ert-deftest test-ai-config-model-to-string-normal-number-returns-formatted ()
+  "Numeric input should be formatted as a string."
+  (should (equal (cj/gptel--model-to-string 42) "42")))
+
+;;; Boundary Cases
+
+(ert-deftest test-ai-config-model-to-string-boundary-empty-string-returns-empty ()
+  "Empty string should be returned as empty string."
+  (should (equal (cj/gptel--model-to-string "") "")))
+
+(ert-deftest test-ai-config-model-to-string-boundary-nil-returns-nil-string ()
+  "Nil is a symbol, so should return \"nil\"."
+  (should (equal (cj/gptel--model-to-string nil) "nil")))
+
+(ert-deftest test-ai-config-model-to-string-boundary-keyword-symbol-includes-colon ()
+  "Keyword symbol should return its name including the colon."
+  (should (equal (cj/gptel--model-to-string :some-model) ":some-model")))
+
+(ert-deftest test-ai-config-model-to-string-boundary-list-uses-format-fallback ()
+  "List input should hit the fallback format branch."
+  (should (equal (cj/gptel--model-to-string '(a b)) "(a b)")))
+
+(ert-deftest test-ai-config-model-to-string-boundary-vector-uses-format-fallback ()
+  "Vector input should hit the fallback format branch."
+  (should (equal (cj/gptel--model-to-string [1 2]) "[1 2]")))
+
+(ert-deftest test-ai-config-model-to-string-boundary-string-with-spaces-unchanged ()
+  "String with spaces should be returned unchanged."
+  (should (equal (cj/gptel--model-to-string "model with spaces") "model with spaces")))
+
+(provide 'test-ai-config-model-to-string)
+;;; test-ai-config-model-to-string.el ends here