public final JdbiExtension withInitializer(JdbiExtensionInitializer initializer) {
        if (initializer == null) {
            throw new IllegalStateException("initializer is null!");
        }

        if (initializerMaybe.isPresent()) {
            throw new IllegalStateException("initializer already defined!");
        }

        this.initializerMaybe = Optional.of(initializer);

        return this;
    }
Sets a {@link JdbiExtensionInitializer} to initialize the {@link Jdbi} instance or the attached data source before running a test.

@return The extension itself for chaining method calls.
testing/src/main/java/org/jdbi/v3/testing/junit5/JdbiExtension.java