Add dbx library: PostgreSQL cluster with master/replica routing, retry, health checking

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dbxtest/dbxtest.go

@@ -0,0 +1,82 @@
+// Package dbxtest provides test helpers for users of the dbx library.
+package dbxtest
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"git.codelab.vc/pkg/dbx"
+)
+
+const (
+	// EnvTestDSN is the environment variable for the test database DSN.
+	EnvTestDSN = "DBX_TEST_DSN"
+	// DefaultTestDSN is the default DSN used when EnvTestDSN is not set.
+	DefaultTestDSN = "postgres://postgres:postgres@localhost:5432/dbx_test?sslmode=disable"
+)
+
+// TestDSN returns the DSN from the environment or the default.
+func TestDSN() string {
+	if dsn := os.Getenv(EnvTestDSN); dsn != "" {
+		return dsn
+	}
+	return DefaultTestDSN
+}
+
+// NewTestCluster creates a Cluster connected to a test database.
+// It skips the test if the database is not reachable.
+// The cluster is automatically closed when the test finishes.
+func NewTestCluster(t testing.TB, opts ...dbx.Option) *dbx.Cluster {
+	t.Helper()
+
+	dsn := TestDSN()
+	cfg := dbx.Config{
+		Master: dbx.NodeConfig{
+			Name: "test-master",
+			DSN:  dsn,
+			Pool: dbx.PoolConfig{MaxConns: 5, MinConns: 1},
+		},
+	}
+	dbx.ApplyOptions(&cfg, opts...)
+
+	ctx := context.Background()
+	cluster, err := dbx.NewCluster(ctx, cfg)
+	if err != nil {
+		t.Skipf("dbxtest: cannot connect to test database: %v", err)
+	}
+
+	t.Cleanup(func() {
+		cluster.Close()
+	})
+
+	return cluster
+}
+
+// TestLogger is a Logger that writes to testing.T.
+type TestLogger struct {
+	T testing.TB
+}
+
+func (l *TestLogger) Debug(_ context.Context, msg string, fields ...any) {
+	l.T.Helper()
+	l.T.Logf("[DEBUG] %s %v", msg, fields)
+}
+
+func (l *TestLogger) Info(_ context.Context, msg string, fields ...any) {
+	l.T.Helper()
+	l.T.Logf("[INFO]  %s %v", msg, fields)
+}
+
+func (l *TestLogger) Warn(_ context.Context, msg string, fields ...any) {
+	l.T.Helper()
+	l.T.Logf("[WARN]  %s %v", msg, fields)
+}
+
+func (l *TestLogger) Error(_ context.Context, msg string, fields ...any) {
+	l.T.Helper()
+	l.T.Logf("[ERROR] %s %v", msg, fields)
+}
+
+// Compile-time check.
+var _ dbx.Logger = (*TestLogger)(nil)