How to change quarkus application configuration with @ConfigMapping in unit tests?

I need to change the quarkus application properties in unit tests to check some negative use cases.

application.properties:

myapp.prop = oldValue

The corresponding property class:

@ConfigMapping(prefix = "myapp")
public interface MyPropertiesMapping {
    String prop();
}

I tried to set the system property in @BeforeAll method and got different results for @ConfigProperty field and @ConfigMapping field.

JUnit test:

@QuarkusTest
class ConfigTest {
    
    @ConfigProperty(name = "myapp.prop")
    String property;

    @Inject
    MyPropertiesMapping myProperites;
    
    @BeforeAll 
    static void changeProperty() {
        System.setProperty("myapp.prop", "newValue");
    }
    
    @AfterAll
    static void clearProperty() {
        System.clearProperty("myapp.prop");
    }
    
    @Test
    void testConfigProperty() {
        Assertions.assertEquals("newValue", property);
    }

    @Test
    void testConfigMapping() {
        Assertions.assertEquals("oldValue", myProperites.prop());
    }

The test shows that property field is set to newValue, but myProperties.prop() still shows oldValue.

So there are 2 questions:

1. Why the behavior of @ConfigProperty and @ConfigMapping is different in the case?
2. How to change values of @ConfigMapping attributes properly?

The difference is that @ConfigMapping it is initialized globally before test classes are executed, and @ConfigProperty injection is local, after the test class is evaluated (since you need the instance to be able to inject it).

If you need to change the configuration for a test, my recommendation is to use @TestProfile and override the configuration with public Map<String, String> getConfigOverrides()instead of setting it up via SystemProperties. If the configuration set via SystemPropertiesis not cleaned correctly, it may leak to other test classes.

Check: https://quarkus.io/guides/getting-started-testing#testing_different_profiles