1 files changed, 109 insertions, 0 deletions
diff --git a/tests/test-prog-json--json-format-buffer.el b/tests/test-prog-json--json-format-buffer.el
new file mode 100644
index 00000000..227eafb9
--- /dev/null
+++ b/tests/test-prog-json--json-format-buffer.el
@@ -0,0 +1,109 @@
+;;; test-prog-json--json-format-buffer.el --- Tests for cj/json-format-buffer -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the cj/json-format-buffer function in prog-json.el.
+;; Tests both the jq path and the built-in fallback path.
+
+;;; Code:
+
+(require 'ert)
+(require 'json)
+(require 'prog-json)
+
+;;; Normal Cases — jq path
+
+(ert-deftest test-prog-json--json-format-buffer-normal-formats-object ()
+  "Compact JSON object is pretty-printed with sorted keys."
+  (with-temp-buffer
+    (insert "{\"zebra\":1,\"alpha\":2}")
+    (cj/json-format-buffer)
+    (should (string= (string-trim (buffer-string))
+                     "{\n  \"alpha\": 2,\n  \"zebra\": 1\n}"))))
+
+(ert-deftest test-prog-json--json-format-buffer-normal-formats-array ()
+  "Compact JSON array is pretty-printed."
+  (with-temp-buffer
+    (insert "[1,2,3]")
+    (cj/json-format-buffer)
+    (should (string= (string-trim (buffer-string))
+                     "[\n  1,\n  2,\n  3\n]"))))
+
+(ert-deftest test-prog-json--json-format-buffer-normal-nested ()
+  "Nested JSON is pretty-printed with sorted keys at all levels."
+  (with-temp-buffer
+    (insert "{\"b\":{\"d\":1,\"c\":2},\"a\":3}")
+    (cj/json-format-buffer)
+    (should (string-match-p "\"a\": 3" (buffer-string)))
+    (should (string-match-p "\"c\": 2" (buffer-string)))
+    ;; "a" should appear before "b" (sorted)
+    (should (< (string-match "\"a\"" (buffer-string))
+               (string-match "\"b\"" (buffer-string))))))
+
+(ert-deftest test-prog-json--json-format-buffer-normal-already-formatted ()
+  "Already-formatted JSON is unchanged."
+  (let ((formatted "{\n  \"alpha\": 1,\n  \"beta\": 2\n}\n"))
+    (with-temp-buffer
+      (insert formatted)
+      (cj/json-format-buffer)
+      (should (string= (buffer-string) formatted)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-prog-json--json-format-buffer-boundary-empty-object ()
+  "Empty JSON object formats cleanly."
+  (with-temp-buffer
+    (insert "{}")
+    (cj/json-format-buffer)
+    (should (string= (string-trim (buffer-string)) "{}"))))
+
+(ert-deftest test-prog-json--json-format-buffer-boundary-empty-array ()
+  "Empty JSON array formats cleanly."
+  (with-temp-buffer
+    (insert "[]")
+    (cj/json-format-buffer)
+    (should (string= (string-trim (buffer-string)) "[]"))))
+
+(ert-deftest test-prog-json--json-format-buffer-boundary-scalar-string ()
+  "Bare JSON string scalar formats without error."
+  (with-temp-buffer
+    (insert "\"hello\"")
+    (cj/json-format-buffer)
+    (should (string= (string-trim (buffer-string)) "\"hello\""))))
+
+(ert-deftest test-prog-json--json-format-buffer-boundary-unicode ()
+  "JSON with unicode characters is preserved."
+  (with-temp-buffer
+    (insert "{\"emoji\":\"\\u2764\",\"name\":\"café\"}")
+    (cj/json-format-buffer)
+    (should (string-match-p "café" (buffer-string)))))
+
+;;; Fallback path — built-in formatter
+
+(ert-deftest test-prog-json--json-format-buffer-fallback-formats-without-jq ()
+  "Falls back to built-in formatter when jq is not found."
+  (cl-letf (((symbol-function 'executable-find) (lambda (_) nil)))
+    (with-temp-buffer
+      (insert "{\"b\":1,\"a\":2}")
+      (cj/json-format-buffer)
+      ;; Built-in formatter should pretty-print (key order may vary)
+      (should (string-match-p "\"a\"" (buffer-string)))
+      (should (string-match-p "\"b\"" (buffer-string)))
+      ;; Should be multi-line (formatted, not compact)
+      (should (> (count-lines (point-min) (point-max)) 1)))))
+
+;;; Error Cases
+
+(ert-deftest test-prog-json--json-format-buffer-error-invalid-json ()
+  "Invalid JSON produces an error, does not silently corrupt buffer."
+  (with-temp-buffer
+    (insert "{not valid json}")
+    (let ((original (buffer-string)))
+      ;; jq will fail on invalid JSON — buffer should not be emptied
+      (condition-case _err
+          (cj/json-format-buffer)
+        (error nil))
+      ;; Buffer should still have content (not wiped)
+      (should (> (length (buffer-string)) 0)))))
+
+(provide 'test-prog-json--json-format-buffer)
+;;; test-prog-json--json-format-buffer.el ends here