In　component-based　software　engineering,　software　systems　are　mainly　constructed　based　on　reusable　components,　such　as　third-party　components　and　in-house　built　components.　Hence,　system　quality　depends　on　the　quality　of　the　involved　components.　Any　change　of　a　component,　it　must　be　re-tested　at　the　unit　level,　and　re-integrated　to　form　component-based　application　systems.　Although　a　number　of　recently　published　papers　address　regression　testing　and　maintenance　of　component-based　systems,　very　few　papers　discuss　how　to　identify　component　changes　and　impacts　at　the　unit　level,　and　find　out　the　reusable　test　cases　in　a　component＇s　test　suite　to　support　its　evolution.　This　paper　focuses　on　component　API-based　changes　and　impacts,　and　proposes　a　systematic　re-test　method　for　software　components　based　on　a　component　API-based　test　model.　The　proposed　method　has　been　implemented　in　a　component　test　tool,　known　as　COMPTest.　It　can　be　used　to　automatically　identify　component-based　API　changes　and　impacts,　as　well　as　reusable　test　cases　in　a　component　test　suite.　The　paper　also　reports　this　tool　and　its　application　results.