refactor(rtt): use proto Duration, add tests

internal/cli/tui/format.go

@@ -0,0 +1,12 @@
+package tui
+
+import (
+	"fmt"
+	"math"
+	"time"
+)
+
+// FormatRTT formats a round-trip time duration as whole milliseconds, e.g. "140ms".
+func FormatRTT(d time.Duration) string {
+	return fmt.Sprintf("%dms", int64(math.Round(float64(d)/float64(time.Millisecond))))
+}

internal/cli/tui/format_test.go

@@ -0,0 +1,32 @@
+package tui
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatRTT(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		in   time.Duration
+		want string
+	}{
+		{"zero", 0, "0ms"},
+		{"rounds down", 39*time.Millisecond + 200*time.Microsecond, "39ms"},
+		{"rounds up at half", 39*time.Millisecond + 500*time.Microsecond, "40ms"},
+		{"rounds up near next ms", 39*time.Millisecond + 600*time.Microsecond, "40ms"},
+		{"exact ms", 140 * time.Millisecond, "140ms"},
+		{"one second", time.Second, "1000ms"},
+		{"1.5s", 1500 * time.Millisecond, "1500ms"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, FormatRTT(tt.in))
+		})
+	}
+}