The degree of testability shows the elegance and maturity of any framework. A more testable system is more maintainable. Spring Framework provides comprehensive support for end-to-end testing of applications for both unit testing as well as integration testing. Spring promotes test-driven development (TDD), facilitates integration testing, and advocates a set of best practices for the unit testing of beans. This is another compelling reason for using Spring to build serious applications.
The POJO-based programming model and loosely coupled nature of Spring beans make it easier to participate in JUnit and TestNG tests even without Spring in the middle. On top of this, Spring provides many testing support components, utilities, and mock objects to make the testing easier.
Spring provides mock implementations of many container-specific components so that the beans can be tested outside a server or container environment. MockEnvironment and MockPropertySource are useful for testing environment-dependent beans. To test beans that depend on HTTP communications, Spring provides mock classes for both client and server sides inside the org.springframework.mock.http and org.springframework.mock.http.client packages.
Another set of useful classes can be found under org.springframework.mock.jndi to run test suites that depend on JNDI resources. The org.springframework.mock.web package contains mock objects for web components based on Servlet 3.0, such as web contexts, filters, controllers, and asynchronous request processing.
Spring ships certain general-purpose and context-specific utilities for unit and integration testing. The org.springframework.test.util package contains a set of utility classes for various testing purposes, including reflection, AOP, JSON, and XML manipulations. Classes under org.springframework.test.web and its nested subdirectories contain a comprehensive set of utility classes to test beans dependent on the web environment. Another set of useful classes for usages specific to ApplicationContext can be found under org.springframework.test.context and its child packages. Their support includes the loading and caching of web, portlet, or application contexts in the test environment; resolving profiles; loading property sources and SQL scripts; managing transactions for test environments; and so on.
The support classes and annotations under the packages listed earlier facilitate the easy and natural testing of Spring applications. A comprehensive discussion over Spring test support is beyond the scope of this book. However, gaining a good understanding of Spring's comprehensive support for unit and integration tests is vital in order to develop elegant code and maintainable applications using Spring.