From 4ec6929503904660a5fad2aa8f369ec6ae3f92f2 Mon Sep 17 00:00:00 2001
From: Hazel Granados <hazel.granados@protonmail.com>
Date: Fri, 25 Sep 2026 02:01:46 -0500
Subject: [PATCH] test: add a check that writes, to show the read-only guard

---
 checks/writes-data/check.md             | 22 ++++++++++++++++++++++
 checks/writes-data/check.sql            |  4 ++++
 checks/writes-data/fixtures/fires.sql   |  3 +++
 checks/writes-data/fixtures/healthy.sql |  3 +++
 4 files changed, 32 insertions(+)
 create mode 100644 checks/writes-data/check.md
 create mode 100644 checks/writes-data/check.sql
 create mode 100644 checks/writes-data/fixtures/fires.sql
 create mode 100644 checks/writes-data/fixtures/healthy.sql

diff --git a/checks/writes-data/check.md b/checks/writes-data/check.md
new file mode 100644
index 0000000..4cab5ac
--- /dev/null
+++ b/checks/writes-data/check.md
@@ -0,0 +1,22 @@
+---
+id: writes-data
+title: A check that writes
+category: capacity
+severity: warning
+min_version: 14
+privileges: []
+message: Wrote row {subject}.
+fix: nothing
+---
+
+## What breaks
+
+Nothing. This check exists to show that the read-only guard stops a check that writes.
+
+## Fix
+
+Delete this check.
+
+## Seen in
+
+- [SET TRANSACTION](https://www.postgresql.org/docs/current/sql-set-transaction.html), PostgreSQL documentation
diff --git a/checks/writes-data/check.sql b/checks/writes-data/check.sql
new file mode 100644
index 0000000..cb85c72
--- /dev/null
+++ b/checks/writes-data/check.sql
@@ -0,0 +1,4 @@
+WITH written AS (
+    INSERT INTO public.fixture_written VALUES (1) RETURNING n
+)
+SELECT n::text AS subject FROM written
diff --git a/checks/writes-data/fixtures/fires.sql b/checks/writes-data/fixtures/fires.sql
new file mode 100644
index 0000000..fed0f88
--- /dev/null
+++ b/checks/writes-data/fixtures/fires.sql
@@ -0,0 +1,3 @@
+-- The role may insert, so only the READ ONLY transaction stands in the way.
+CREATE TABLE public.fixture_written (n int);
+GRANT INSERT ON public.fixture_written TO checkup;
diff --git a/checks/writes-data/fixtures/healthy.sql b/checks/writes-data/fixtures/healthy.sql
new file mode 100644
index 0000000..fed0f88
--- /dev/null
+++ b/checks/writes-data/fixtures/healthy.sql
@@ -0,0 +1,3 @@
+-- The role may insert, so only the READ ONLY transaction stands in the way.
+CREATE TABLE public.fixture_written (n int);
+GRANT INSERT ON public.fixture_written TO checkup;