Override a property for a single Spring Boot test

Your properties are evaluated by Spring during the Spring context loading.
So you cannot change them after the container has started.

As workaround, you could split the methods in multiple classes that so would create their own Spring context. But beware as it may be a bad idea as tests execution should be fast.

A better way could be having a setter in the class under test that injects the some.property value and using this method in the test to change programmatically the value.

private String someProperty;

@Value("${some.property}")
public void setSomeProperty(String someProperty) {
    this.someProperty = someProperty;
}

Update

Possible at least with Spring 5.2.5 and Spring Boot 2.2.6

@DynamicPropertySource
static void dynamicProperties(DynamicPropertyRegistry registry) {
    registry.add("some.property", () -> "valueA");
}