Running assertions on the aggregate after given/when/then

[wikando-ck]

Context
We use public private(set) $properties on our aggregates.
These are modified via the apply*-methods.
They just expose the aggregates current state instead of having getters.

Using given/when/then, we can only assert that the right events are created on a given aggregate when something is called.
To cover the correctness of the apply-methods, we also need to assert on the exposed state of the aggregate.

I see two ways of having that:

• Add a new method that can receive a callback, which can run assertions and can use variables from the setup scope.
• Allow callbacks passed into then(), which will behave in the same way.

Example

$this
    ->given(
        new ProfileCreated(
            ProfileId::fromString('1'),
            Email::fromString('hq@patchlevel.de'),
        ),
    )
    ->when(static fn (Profile $profile) => $profile->visitProfile(ProfileId::fromString('2')))
    ->then(
        new ProfileVisited(ProfileId::fromString('2')),
        // passing a callback, requires a union-type for `then()`
        static fn (Profile $profile) => $this->assertSame(ProfileId::fromString('1'), $profile->id))
    )
    // or with a method, but this would break the "standard" given-when-then
    ->thenCallback(static fn (Profile $profile) => $this->assertSame(ProfileId::fromString('1'), $profile->id)))
;
}

Right now PHPUnit assertions can only be ran in the when(), due to the execution phase using after.
Or am i missing something here?