With Label1 declared as B4XView and MultiLine
Dim su As StringUtils 'Add this library in project
If su.MeasureMultilineTextHeight(Label1.As(Label), Label1.Text) > Label1.Height Then
Log("TRUNCATED")
Else
Log("OK")
End If
If SingleLine Label (always declared as B4xView)
Dim bc As B4XCanvas
bc.Initialize(Label1)
Dim r As B4XRect = bc.MeasureText(Label1.Text, Label1.Font)
If r.Width > Label1.Width Then
Log("TRUNCATED")
Else
Log("OK")
End If
Depending on TextSize, Label size and so on it can be more or less accurate.