Prevent duplicate post submissions

internal/web/posts_test.go

@@ -458,6 +458,8 @@ func TestQuestionPageRendersNestedPostControls(t *testing.T) {
 		"Shop response",
 		"Edited",
 		`action="/posts"`,
+		`data-submit-once`,
+		`data-submit-button`,
 		`action="/posts/` + root.ID + `/edit"`,
 		`action="/posts/` + homeownerReply.ID + `/edit"`,
 		`>The model number is 123A.</textarea>`,

internal/web/server_test.go

@@ -168,6 +168,16 @@ func TestRegisterLoginAsk(t *testing.T) {
 	if rec.Code != 200 {
 		t.Fatalf("submit form %d", rec.Code)
 	}
+	for _, want := range []string{
+		`src="/static/app.js"`,
+		`id="submit-progress"`,
+		`data-submit-once`,
+		`data-submit-button`,
+	} {
+		if !strings.Contains(rec.Body.String(), want) {
+			t.Fatalf("submit form missing %q: %s", want, rec.Body.String())
+		}
+	}
 	csrf := csrfFrom(rec.Body.String())
 	form := strings.NewReader("_csrf=" + csrf + "&title=Leaky+faucet&body=Drip+all+night.&city=Oakland")
 	req = httptest.NewRequest(http.MethodPost, "/submit", form)