test: add test database cleaner in subprocess (#19844)

fixes https://github.com/coder/internal/issues/927

Adds a small subprocess that outlives the testing process to clean up any leaked test databases.

coderd/database/dbtestutil/postgres_test.go

@@ -3,6 +3,7 @@ package dbtestutil_test
 import (
 	"database/sql"
 	"testing"
+	"time"
 
 	_ "github.com/lib/pq"
 	"github.com/stretchr/testify/require"
@@ -110,3 +111,27 @@ func TestOpen_ValidDBFrom(t *testing.T) {
 	require.True(t, rows.Next())
 	require.NoError(t, rows.Close())
 }
+
+func TestOpen_Panic(t *testing.T) {
+	t.Skip("unskip this to manually test that we don't leak a database into postgres")
+	t.Parallel()
+	if !dbtestutil.WillUsePostgres() {
+		t.Skip("this test requires postgres")
+	}
+
+	_, err := dbtestutil.Open(t)
+	require.NoError(t, err)
+	panic("now check SELECT datname FROM pg_database;")
+}
+
+func TestOpen_Timeout(t *testing.T) {
+	t.Skip("unskip this and set a short timeout to manually test that we don't leak a database into postgres")
+	t.Parallel()
+	if !dbtestutil.WillUsePostgres() {
+		t.Skip("this test requires postgres")
+	}
+
+	_, err := dbtestutil.Open(t)
+	require.NoError(t, err)
+	time.Sleep(11 * time.Minute)
+}