test: guard walkthrough.repl against public API drift

test/state_flow/walkthrough_test.clj

@@ -0,0 +1,31 @@
+(ns state-flow.walkthrough-test
+  "Guards doc/walkthrough.repl against silent drift from the public API (#107)."
+  (:require [clojure.java.io :as io]
+            [clojure.string :as string]
+            [clojure.test :refer [deftest is testing]]
+            [state-flow.api :as flow]))
+
+(def walkthrough-path "doc/walkthrough.repl")
+
+(deftest walkthrough-file-exists
+  (is (.exists (io/file walkthrough-path))
+      (str "expected " walkthrough-path " to exist")))
+
+(deftest walkthrough-references-current-public-api
+  (testing "symbols shown in the walkthrough still resolve on state-flow.api"
+    (let [body (slurp walkthrough-path)
+          required-snippets ["flow/swap-state"
+                             "flow/get-state"
+                             "match?"
+                             "(flow \""
+                             "(run"]]
+      (doseq [snippet required-snippets]
+        (is (string/includes? body snippet)
+            (str "walkthrough should mention " (pr-str snippet))))
+      (doseq [sym '[state-flow.api/swap-state
+                    state-flow.api/get-state
+                    state-flow.api/run
+                    state-flow.api/match?
+                    state-flow.api/flow]]
+        (is (some? (resolve sym))
+            (str "API var missing: " sym))))))