Replace #Value property within #Configuration during Spring Boot test - testing

Question

Scenario
I've got a Spring Boot application with a #Configuration annotated Spring configuration class which contains some #Value annotated fields. For testing I want to replace these field values with custom test values.
Unfortunately these test values cannot be overridden using a simple properties file, (String) constants or similar, instead I must use some custom written property resolving Java class (e.g. TargetProperties.getProperty("some.username")).
The problem I have is that when I add a custom PropertySource to the ConfigurableEnvironment within my test configuration, it's already too late because this PropertySource will be added after the e.g. RestTemplate has been created.
Question
How can I override #Value annotated fields within a #Configuration class with properties obtained programmatically via custom Java code before anything else gets initialized?
Code
Production Configuration Class
#Configuration
public class SomeConfiguration {
#Value("${some.username}")
private String someUsername;
#Value("${some.password}")
private String somePassword;
#Bean
public RestTemplate someRestTemplate() {
RestTemplate restTemplate = new RestTemplate();
restTemplate.getInterceptors().add(
new BasicAuthorizationInterceptor(someUsername, somePassword));
return restTemplate;
}
}
Test Configuration Class
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class SomeTest {
#SpringBootConfiguration
#Import({MySpringBootApp.class, SomeConfiguration.class})
static class TestConfiguration {
#Autowired
private ConfigurableEnvironment configurableEnvironment;
// This doesn't work:
#Bean
#Lazy(false)
// I also tried a #PostConstruct method
public TargetPropertiesPropertySource targetPropertiesPropertySource() {
TargetPropertiesPropertySource customPropertySource =
new TargetPropertiesPropertySource();
configurableEnvironment.getPropertySources().addFirst(customPropertySource);
return customPropertySource;
}
}
}

Answer 1

You can override properties directly in the #SpringBootTest annotation using the properties parameter:
#SpringBootTest(properties = {"some.username=user", "some.password=pwd"},
webEnvironment = SpringBootTest.WebEnvironment.NONE)

Answer 2

You can use #TestPropertySource
#TestPropertySource(
properties = {
"some.username=validate",
"some.password=false"
}
)
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
public class ApplicationTest {
//...
}

Answer 3

You can use constructor injection in production cases, which allows it to set the configuration manually:
#Configuration
public class SomeConfiguration {
private final String someUsername;
private final String somePassword;
#Autowired
public SomeConfiguration(#Value("${some.username}") String someUsername,
#Value("${some.password}") String somePassword) {
this.someUsername = someUsername;
this.somePassword = somePassword;
}
...
)
}
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class SomeTest {
private SomeConfiguration config;
#Before
public init() {
config = new SomeConfiguration("foo", "bar");
}
}