ConfigurationProperites not applied in SpringBootTest?

Question

We have the following configuration properties class (reduced the minimum)

@ConstructorBinding
@ConfigurationProperties(prefix = "prefix")
data class MyConfiguraion(
    val mapping: MutableMap<String, Map<String, Int>>
)

The configuration in the application yaml looks like this:

prefix.mapping:
   value1: 
     a: 1
     b: 2

using the application.yml, the map is passed correctly, though if I want to test it with SpringBootTest, the map is not passed, instead an empty map is passed to the constructor:

@SpringBootTest(
    classes = [MyConfiguraion::class, ],
    properties = [
        "prefix.mapping.value1.a=1",
        "prefix.mapping.value1.b=2",

    ]
)
internal class CapabilityMappingTest {

    @Autowired
    lateinit var config: MyConfiguraiton

    @Test
    fun `mapping was correctly appiled`() {

        expectThat(config)
            .get { mapping }.and {
                get("value1")
                    .isNotNull()
                    .and {
                        get("a") isEqualTo 1
                        get("b") isEqualTo 2
       
            }
    }
}

(Example is reduced to a minimum to show the issue. Without the context, it does not look useful)