Fix flaky mysqlctl blackbox test (#17387)

go/vt/logutil/logger.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"runtime"
+	"slices"
 	"strings"
 	"sync"
 	"time"
@@ -246,6 +247,12 @@ func (ml *MemoryLogger) Clear() {
 	ml.mu.Unlock()
 }
 
+func (ml *MemoryLogger) LogEvents() []*logutilpb.Event {
+	ml.mu.Lock()
+	defer ml.mu.Unlock()
+	return slices.Clone(ml.Events)
+}
+
 // LoggerWriter is an adapter that implements the io.Writer interface.
 type LoggerWriter struct {
 	logger Logger

go/vt/mysqlctl/blackbox/utils.go

@@ -78,7 +78,7 @@ func GetStats(stats *backupstats.FakeStats) StatSummary {
 
 func AssertLogs(t *testing.T, expectedLogs []string, logger *logutil.MemoryLogger) {
 	for _, log := range expectedLogs {
-		require.Truef(t, slices.ContainsFunc(logger.Events, func(event *logutilpb.Event) bool {
+		require.Truef(t, slices.ContainsFunc(logger.LogEvents(), func(event *logutilpb.Event) bool {
 			return event.GetValue() == log
 		}), "%s is missing from the logs", log)
 	}