spring boot test启动过程

加载Spring的上下文启动流程

https://www.processon.com/embed/61cd2436e401fd7a538b36a7
解析：

@SpringBootTest标记了junit5的注解@ExtendWith(SpringExtension.class)

SpringExtension实现了junit5的test的生命周期的钩子函数，如BeforeAllCallback，TestInstancePostProcessor，BeforeEachCallback

在junit5的钩子函数中BeforeAllCallback会实例化TestContextManager

TestContextManager的钩子函数会解析@SpringBootTest的元注解@BootstrapWith(SpringBootTestContextBootstrapper.class)，进而获取到关键类SpringBootContextLoader

TestContextManager也会通过spring的SPI机制解析meta-INF/spring.factories获取所有实现TestExecutionListener的接口实现类,
关键类ServletTestExecutionListener-针对servletweb类型

test生命周期钩子函数调用TestExecutionListener的方法，进而会触发执行ServletTestExecutionListener的setUpRequestContextIfNecessary
setUpRequestContextIfNecessary

会从缓存中获取ApplicationContext，没有最终调用SpringBootContextLoader.loadContext
加载spring的上下文

SpringBootContextLoader.loadContext会获取上面解析配置推测的类型，最终执行SpringApplication.run启动spring
boot加载spring的上下文

public class SpringBootContextLoader extends AbstractContextLoader {

	public class SpringBootContextLoader extends AbstractContextLoader {
    
	@Override
	public ApplicationContext loadContext(MergedContextConfiguration config) throws Exception {
		Class[] configClasses = config.getClasses();
		String[] configLocations = config.getLocations();
		Assert.state(!ObjectUtils.isEmpty(configClasses) || !ObjectUtils.isEmpty(configLocations),
				() -> "No configuration classes or locations found in @SpringApplicationConfiguration. "
						+ "For default configuration detection to work you need Spring 4.0.3 or better (found "
						+ SpringVersion.getVersion() + ").");
		SpringApplication application = getSpringApplication();
		application.setMainApplicationClass(config.getTestClass());
		application.addPrimarySources(Arrays.asList(configClasses));
		application.getSources().addAll(Arrays.asList(configLocations));
		List> initializers = getInitializers(config, application);
		if (config instanceof WebMergedContextConfiguration) {
			application.setWebApplicationType(WebApplicationType.SERVLET);
			if (!isEmbeddedWebEnvironment(config)) {
				new WebConfigurer().configure(config, application, initializers);
			}
		}
		else if (config instanceof ReactiveWebMergedContextConfiguration) {
			application.setWebApplicationType(WebApplicationType.REACTIVE);
			if (!isEmbeddedWebEnvironment(config)) {
				application.setApplicationContextFactory(
						ApplicationContextFactory.of(GenericReactiveWebApplicationContext::new));
			}
		}
		else {
			application.setWebApplicationType(WebApplicationType.NONE);
		}
		application.setInitializers(initializers);
		ConfigurableEnvironment environment = getEnvironment(application, config.getActiveProfiles());
		ResourceLoader resourceLoader = (application.getResourceLoader() != null) ? application.getResourceLoader()
				: new DefaultResourceLoader(null);
		TestPropertySourceUtils.addPropertiesFilesToEnvironment(environment, resourceLoader,
				config.getPropertySourceLocations());
		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(environment, getInlinedProperties(config));
		application.setEnvironment(environment);
		String[] args = SpringBootTestArgs.get(config.getContextCustomizers());
		return application.run(args);
	}
    ...
 }