diff --git a/divergence_test.go b/divergence_test.go
new file mode 100644
index 0000000..2f0f7be
--- /dev/null
+++ b/divergence_test.go
@@ -0,0 +1,131 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+// fakeNoulJev answers every question in a request with a fixed noul probability.
+func fakeNoulJev(t *testing.T, noul float64) *JevClient {
+	t.Helper()
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var body struct {
+			Questions map[string]any `json:"questions"`
+		}
+		json.NewDecoder(r.Body).Decode(&body)
+		out := map[string]any{}
+		for q := range body.Questions {
+			out[q] = map[string]any{"type": "noul", "noul": noul}
+		}
+		json.NewEncoder(w).Encode(map[string]any{"model": "jev-1.14.0", "answers": out,
+			"usage": map[string]int{"input_tokens": 40, "output_tokens": 0}})
+	}))
+	t.Cleanup(srv.Close)
+	return &JevClient{url: srv.URL, key: "tk", model: "jev-latest", threshold: 0.7, client: srv.Client()}
+}
+
+func postDeliver(t *testing.T, ts *httptest.Server, id, author, refersTo, text string) string {
+	t.Helper()
+	code, out := post(t, ts.URL+"/api/nests/"+id+"/messages",
+		`{"author":"`+author+`","kind":"deliver","refers_to":"`+refersTo+`","text":"`+text+`"}`)
+	if code != http.StatusCreated {
+		t.Fatalf("deliver %s: %d %v", author, code, out)
+	}
+	return out["msg_id"].(string)
+}
+
+func findNudge(ts *httptest.Server, id, target string) map[string]any {
+	for _, m := range nestMessagesNoT(ts, id) {
+		if m["kind"] == "nudge" && m["refers_to"] == target {
+			return m
+		}
+	}
+	return nil
+}
+
+func nestMessagesNoT(ts *httptest.Server, id string) []map[string]any {
+	resp, err := http.Get(ts.URL + "/api/nests/" + id + "/messages")
+	if err != nil {
+		return nil
+	}
+	defer resp.Body.Close()
+	var msgs []map[string]any
+	json.NewDecoder(resp.Body).Decode(&msgs)
+	return msgs
+}
+
+func waitForNudge(ts *httptest.Server, id, target string) map[string]any {
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		if n := findNudge(ts, id, target); n != nil {
+			return n
+		}
+		if time.Now().After(deadline) {
+			return nil
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+func TestRestatementGetsNudge(t *testing.T) {
+	ts, s := newTestNestServer(t)
+	s.p.Flock.SetClassifier(fakeNoulJev(t, 0.8)) // above band 0.7
+	id := newNest(t, ts, "Lab", `"Hugin","Munin"`)
+	r := postRequest(t, ts, id, "conspiracy", "is this risky")
+	postDeliver(t, ts, id, "Hugin", r, "ship it")
+	d2 := postDeliver(t, ts, id, "Munin", r, "also ship it")
+
+	n := waitForNudge(ts, id, d2)
+	if n == nil {
+		t.Fatalf("restated deliver must get a nudge, log: %+v", s.msgs.All(id))
+	}
+	if n["to"] != "Munin" || n["author"] != "harness" {
+		t.Fatalf("nudge must address the restating crow from the harness, got %v", n)
+	}
+	if !containsMsg(s.msgs.All(id), d2) {
+		t.Fatal("the restated deliver itself must stay in the log")
+	}
+}
+
+func TestDistinctDeliversNoNudge(t *testing.T) {
+	ts, s := newTestNestServer(t)
+	s.p.Flock.SetClassifier(fakeNoulJev(t, 0.2)) // below band
+	id := newNest(t, ts, "Lab", `"Hugin","Munin"`)
+	r := postRequest(t, ts, id, "conspiracy", "is this risky")
+	postDeliver(t, ts, id, "Hugin", r, "ship it")
+	d2 := postDeliver(t, ts, id, "Munin", r, "wait for the audit")
+	time.Sleep(300 * time.Millisecond)
+	if n := findNudge(ts, id, d2); n != nil {
+		t.Fatalf("a distinct deliver must not be nudged, got %v", n)
+	}
+}
+
+func TestNudgeSpendsNoModelTokens(t *testing.T) {
+	ts, s := newTestNestServer(t)
+	s.p.Flock.SetClassifier(fakeNoulJev(t, 0.8))
+	id := newNest(t, ts, "Lab", `"Hugin","Munin"`)
+	r := postRequest(t, ts, id, "conspiracy", "is this risky")
+	postDeliver(t, ts, id, "Hugin", r, "ship it")
+
+	d2, err := s.msgs.Append(Message{NestID: id, Kind: "deliver", Author: "Munin", Text: "ship", RefersTo: r, Timestamp: time.Now().UTC().Format(time.RFC3339)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	b := &Budget{name: "nest", limit: 1}
+	s.checkDivergence(nestOf(s, id), d2, b)
+	if b.Spent() != 0 {
+		t.Fatalf("a review nudge must spend no model tokens, spent=%d", b.Spent())
+	}
+}
+
+func containsMsg(msgs []Message, msgID string) bool {
+	for _, m := range msgs {
+		if m.MsgID() == msgID {
+			return true
+		}
+	}
+	return false
+}