Since components are the major building blocks for component-based systems, developing high quality components is becoming very critical for in component-based software engineering. To generate high quality components, we must pay attention to component testability to ensure that reusable components not only can be tested by component vendors, but also can be easily validated by component users. Therefore, component testability analysis, verification and measurement become very important research topic in testing components and component-based systems. This paper discusses the component testability in a quantifiable approach based on a component testability analysis model. Engineers can use this model to verify and measure component testability during a component development process. Based on this testability model, the paper discusses component testability verification, and proposes a pentagram model for testability measurement.