老师，以下问题怎么解决？

ERROR org.springframework.test.context.TestContextManager - Caught exception while allowing TestExecutionListener [org.springframework.test.context.support.DependencyInjectionTestExecutionListener@49c43f4e] to prepare test instance [com.imooc.o2o.dao.AreaDaoTest@4f9a3314]
java.lang.IllegalStateException: Failed to load ApplicationContext

Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name ‘dataSource’ defined in class path resource [spring/spring-dao.xml]: Could not resolve placeholder ‘jdbc.username’ in value “{jdbc.username}”; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder ‘jdbc.username’ in value “{jdbc.username}”

Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder ‘jdbc.username’ in value “${jdbc.username}”