Add replication handler tests

pkg/wal/replication/postgres/helper_test.go

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package postgres
+
+import (
+	"errors"
+	"fmt"
+	"time"
+)
+
+type mockRow struct {
+	lsn    string
+	lag    int64
+	scanFn func(args ...any) error
+}
+
+func (m *mockRow) Scan(args ...any) error {
+	if m.scanFn != nil {
+		return m.scanFn(args...)
+	}
+
+	switch arg := args[0].(type) {
+	case *string:
+		*arg = m.lsn
+	case *int64:
+		*arg = m.lag
+	default:
+		return fmt.Errorf("unexpected argument type in scan: %T", args[0])
+	}
+
+	return nil
+}
+
+const (
+	testDBName = "test-db"
+	testSlot   = "test_slot"
+	testLSN    = uint64(7773397064)
+	testLSNStr = "1/CF54A048"
+)
+
+var (
+	errTest = errors.New("oh noes")
+
+	now = time.Now()
+)