test: add gloss-fetch test suite (red phase)

Eight test files cover the network layer's public and internal contract.
The boundary mock is `url-retrieve-synchronously', wrapped by a small
`testutil-gloss-fetch' helper that builds response buffers in the shape
the url library returns.

Tests cover the 200 happy paths (anaphora and SBIR fixtures), 404 to
:no-defs, 5xx and 4xx-other and malformed JSON to :server-error, 429 to
:rate-limited, nil-from-url to :unreachable, the libxml availability
probe (one-shot, signals user-error when absent), the registry walker
ordering, and the pure HTML strip helper across N/B/E.

Tests fail on missing `gloss-fetch--*' functions, as expected for red
phase.

1 files changed, 62 insertions, 0 deletions

diff --git a/tests/test-gloss-fetch--libxml-probe.el b/tests/test-gloss-fetch--libxml-probe.el
new file mode 100644
index 0000000..830a278
--- /dev/null
+++ b/tests/test-gloss-fetch--libxml-probe.el
@@ -0,0 +1,62 @@
+;;; test-gloss-fetch--libxml-probe.el --- libxml availability probe tests -*- lexical-binding: t -*-
+
+;; SPDX-License-Identifier: GPL-3.0-or-later
+
+;;; Commentary:
+;; libxml is a precondition for online fetch.  First call probes once;
+;; absent libxml triggers a one-shot `user-error' and disables online
+;; fetch package-wide for the session.  Subsequent attempts in the same
+;; session also signal `user-error'.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'gloss-fetch)
+(require 'testutil-gloss-fetch)
+
+(ert-deftest test-gloss-fetch-libxml-absent-signals-user-error ()
+  "Error: with libxml unavailable, the first fetch signals user-error and disables online."
+  (let ((gloss-fetch--libxml-disabled nil))
+    (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
+               (lambda () nil)))
+      (should-error (gloss-fetch-definitions "anything") :type 'user-error)
+      ;; Subsequent attempts also signal — no auto-recovery in the same session.
+      (should-error (gloss-fetch-definitions "again") :type 'user-error))))
+
+(ert-deftest test-gloss-fetch-libxml-error-mentions-libxml2 ()
+  "Error: the user-error message names libxml2 so the user can act."
+  (let ((gloss-fetch--libxml-disabled nil))
+    (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
+               (lambda () nil)))
+      (let ((err (should-error (gloss-fetch-definitions "x") :type 'user-error)))
+        (should (string-match-p "libxml2" (error-message-string err)))))))
+
+(ert-deftest test-gloss-fetch-libxml-probe-runs-only-once ()
+  "Boundary: the libxml availability probe is invoked at most once per session."
+  (let ((probe-calls 0)
+        (gloss-fetch--libxml-disabled nil)
+        (gloss-fetch--libxml-checked nil))
+    (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
+               (lambda () (cl-incf probe-calls) t)))
+      (gloss-fetch-test--with-mocked-url
+          (lambda (_url) (gloss-fetch-test--ok-response "{}"))
+        (gloss-fetch-definitions "first")
+        (gloss-fetch-definitions "second")
+        (gloss-fetch-definitions "third"))
+      (should (= 1 probe-calls)))))
+
+(ert-deftest test-gloss-fetch-libxml-present-allows-fetch ()
+  "Normal: when libxml is available, fetch proceeds normally."
+  (let ((gloss-fetch--libxml-disabled nil)
+        (gloss-fetch--libxml-checked nil))
+    (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
+               (lambda () t)))
+      (gloss-fetch-test--with-mocked-url
+          (lambda (_url) (gloss-fetch-test--ok-response "{}"))
+        (let ((result (gloss-fetch-definitions "term")))
+          (should (eq (car result) :empty))
+          (should (member 'wiktionary (plist-get result :no-defs))))))))
+
+(provide 'test-gloss-fetch--libxml-probe)
+;;; test-gloss-fetch--libxml-probe.el ends here