DatabaseTestExtension.kt

class DatabaseTestExtension : ParameterResolver {
    private val STORE_NAME = "main-database"

    override fun supportsParameter(parameterContext: ParameterContext, extensionContext: ExtensionContext?): Boolean {
        return parameterContext.parameter.type == Database::class.java
    }

    override fun resolveParameter(parameterContext: ParameterContext, extensionContext: ExtensionContext): Any {
        // We do the store thing here to avoid loading and migrating the DB for each test/class
        // Will however load per thread, so are not guaranteed to be done only once
        val store = extensionContext.root.getStore(Namespace.create(DatabaseTestExtension::class.java.simpleName))
        val db: Database = (store.get(STORE_NAME) as Database?) ?: Database(Config.load()).also {
            // New object so do initialization and store
            it.initializeAndMigrate()
            store.put(STORE_NAME, it)
        }
        return db
    }
}