The Actual Different: Spring boot #ComponentScan vs #Import when involving ConditionalOnClass - spring

Question

Context
I know there are a lot of posts regarding the comparison between these two. All of them just focus on #Import works on single Config file while #ComponenentScan will scan all config, bean, service files.
I find something new, hope someone can give me a good explanation behind this:
Prerequisite Artifact:
org.springframework.boot.autoconfigure
org.springframework.boot.test
#SpringBootTest(classes = test1char.class)
#ComponentScan("org.springframework.boot.autoconfigure.jackson")
//#SpringBootTest(classes = test1char.class)
//#Import(org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration.class)
public class ObjectMapperTest {
//cannot autowired: no such bean when using ComponenentScan
// Can autowired when either using #Import
// or #SpringBootTest(classes = org.springframework.boot.autoconfigure.jackson.class)
#Autowired
ObjectMapper objectMapper;
#Test
void main() {
var date = LocalDateTime.now();//LocalDateTime
String s;
try {
s = objectMapper.writeValueAsString(date);
System.out.println(s);
}catch (JsonProcessingException e){
System.out.println(e);
}
}
}
ObjectMapper bean producer class:
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration.class for reference
#AutoConfiguration
#ConditionalOnClass({ObjectMapper.class})
public class JacksonAutoConfiguration {
.... omit
#Configuration(
proxyBeanMethods = false
)
#ConditionalOnClass({Jackson2ObjectMapperBuilder.class})
static class JacksonObjectMapperConfiguration {
JacksonObjectMapperConfiguration() {
}
#Bean
#Primary
#ConditionalOnMissingBean
ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
return builder.createXmlMapper(false).build();
}
}
Issue
Basically the ObjectMapper cannot autowired: no such bean when using ComponenentScan. But it can be autowired when either using #Import or #SpringBootTest(classes = org.springframework.boot.autoconfigure.jackson.class)
Note: test1char.class is just a dummy class so that it has a context while not using the default SpringBootApplication which has everything in class path
I know it must have something to do with ConditionalOnClass which requires some class in jar org.springframework.boot.autoconfigure.jackson to be in classpath. So I boldly guess only #Import and #SprngBoot and #SpringBootTest can load class or package to be in classpath?
That's why quite often ObjectMapper cannot be autoconfigured in #SpringBootTest annotated integration test as we often forgot to add the jar to it.
Update
Hate to say with #EnableAutoConfiguration it works all good like below:
#ComponentScan("org.springframework.boot.autoconfigure.jackson")
#EnableAutoConfiguration
Update
Actually #EnableAutoConfiguration alone also works without #ComponentScan.
-- One who is always confused by SpringBoot config xD
Attachment: Condition Report output in Intellij when using #ComponenetScan
============================
CONDITIONS EVALUATION REPORT
Positive matches:
None
Negative matches:
None
Exclusions:
None
Unconditional classes:
None