1 files changed, 40 insertions, 0 deletions
diff --git a/internal/file/flags_test.go b/internal/file/flags_test.go
new file mode 100644
index 0000000..120e432
--- /dev/null
+++ b/internal/file/flags_test.go
@@ -0,0 +1,40 @@
+package file
+
+import (
+	"strings"
+	"sync"
+	"syscall"
+	"testing"
+)
+
+func TestFlagsBuildStringConcurrent(t *testing.T) {
+	flagsToHumanCache = sync.Map{}
+
+	const workers = 32
+	const iterations = 500
+	const want = "O_WRONLY|O_APPEND"
+	flag := Flags(syscall.O_WRONLY | syscall.O_APPEND)
+
+	var wg sync.WaitGroup
+	errs := make(chan string, workers)
+	for i := 0; i < workers; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < iterations; j++ {
+				var sb strings.Builder
+				flag.BuildString(&sb)
+				if got := sb.String(); got != want {
+					errs <- got
+					return
+				}
+			}
+		}()
+	}
+	wg.Wait()
+	close(errs)
+
+	for got := range errs {
+		t.Fatalf("unexpected BuildString output %q, want %q", got, want)
+	}
+}