Add Kotlin DSL extension functions for TestEntityManager

[csikb]

Consider adding Kotlin DSL extension functions for TestEntityManager.

package org.springframework.boot.test.autoconfigure.orm.jpa

inline fun <reified T> TestEntityManager.find(primaryKey: Any?): T {
    return this.find(T::class.java, primaryKey)
}

inline fun <reified T> TestEntityManager.persistAndGetId(entity: Any): T {
    return this.persistAndGetId(entity, T::class.java)
}

inline fun <reified T> TestEntityManager.getId(entity: Any): T {
    return this.getId(entity, T::class.java)
}

There are possibly more classes that could be considered to add Kotlin DSL functions for.
This change would enhance the Kotlin experience when using this library :)

[vineet005]

Instead of just adding Kotlin DSL extension functions directly to TestEntityManager, wrap it in a dedicated Kotlin-first testing module that leverages delegation and inline reified generics.

Example Implementation:

class KTestEntityManager(private val delegate: TestEntityManager) {

    inline fun <reified T> find(id: Any?): T? =
        delegate.find(T::class.java, id)

    inline fun <reified T> persistAndGetId(entity: T): Any? {
        delegate.persist(entity)
        return delegate.getId(entity)
    }

    inline fun <reified T> getId(entity: T): Any? =
        delegate.getId(entity)
    
    fun <T> persistAll(vararg entities: T) {
        entities.forEach { delegate.persist(it) }
    }

    inline fun <reified T> refresh(entity: T) {
        delegate.refresh(entity)
    }
}

---

It will keep TestEntityManager untouched, while offering a Kotlin-first wrapper, will eliminate the need for explicit class reference, can also add Kotlin idiomatic functions like persistAll(vararg entities), Developers can inject KTestEntityManager instead of TestEntityManager in Kotlin test classes.

---

Example Usage:

val em = KTestEntityManager(testEntityManager)

val user = User("Alice")
val id = em.persistAndGetId(user)

val fetched = em.find<User>(id)
em.refresh(fetched!!)

This approach solves the problem more holistically: instead of sprinkling Kotlin DSL extensions across TestEntityManager, it provides a dedicated Kotlin testing utility layer that can evolve independently and stay idiomatic.

[wilkinsona]

Superseded by #49063.