test: implement unit test to excercise pg connection deadlock

Emyrk · Emyrk · commit 89f5828bd9b6 · 2025-06-24T20:08:12.000-05:00
diff --git a/coderd/database/dbtestutil/db.go b/coderd/database/dbtestutil/db.go
@@ -36,6 +36,7 @@ type options struct {
 	returnSQLDB   func(*sql.DB)
 	logger        slog.Logger
 	url           string
+	maxConns      int
 }
 
 type Option func(*options)
@@ -66,6 +67,12 @@ func WithURL(u string) Option {
 	}
 }
 
+func WithMaxConns(maxConns int) Option {
+	return func(o *options) {
+		o.maxConns = maxConns
+	}
+}
+
 func withReturnSQLDB(f func(*sql.DB)) Option {
 	return func(o *options) {
 		o.returnSQLDB = f
@@ -137,12 +144,16 @@ func NewDB(t testing.TB, opts ...Option) (database.Store, pubsub.Pubsub) {
 		t.Cleanup(func() {
 			_ = sqlDB.Close()
 		})
+
 		if o.returnSQLDB != nil {
 			o.returnSQLDB(sqlDB)
 		}
 		if o.dumpOnFailure {
 			t.Cleanup(func() { DumpOnFailure(t, connectionURL) })
 		}
+		if o.maxConns > 0 {
+			sqlDB.SetMaxOpenConns(o.maxConns)
+		}
 		// Unit tests should not retry serial transaction failures.
 		db = database.New(sqlDB, database.WithSerialRetryCount(1))
 
diff --git a/coderd/files/cache_test.go b/coderd/files/cache_test.go
@@ -26,6 +26,36 @@ import (
 	"github.com/coder/coder/v2/testutil"
 )
 
+func TestPGConn(t *testing.T) {
+	t.Parallel()
+
+	// This test is just to ensure that the Postgres connection is working.
+	// It does not test the cache itself, but rather the underlying database
+	// connection.
+	db, _ := dbtestutil.NewDB(t, dbtestutil.WithMaxConns(1))
+	cache := files.New(prometheus.NewRegistry(), &coderdtest.FakeAuthorizer{})
+
+	//nolint:gocritic // Unit testing
+	ctx := dbauthz.AsFileReader(testutil.Context(t, testutil.WaitShort))
+	file := dbgen.File(t, db, database.File{})
+
+	// Consume a pg connection with a transaction.
+	tx := dbtestutil.StartTx(t, db, nil)
+
+	// Acquire the file from the cache outside the transaction.
+	fs, err := cache.Acquire(ctx, db, file.ID)
+	require.NoError(t, err)
+	defer fs.Close()
+
+	// Acquire the file from the cache inside the transaction.
+	fs2, err := cache.Acquire(ctx, tx, file.ID)
+	require.NoError(t, err)
+	defer fs2.Close()
+	require.NoError(t, tx.Done()) // Close the transaction
+
+	require.Equal(t, 1, cache.Count())
+}
+
 // nolint:paralleltest,tparallel // Serially testing is easier
 func TestCacheRBAC(t *testing.T) {
 	t.Parallel()
