How Custom Metadata should be usable in Apex

WriteMetadata.java

@IsTest
private class CustomMetadataInApex_Test {
    
    @IsTest
    private static void workLikeCustomObject() {
      insert new ProductSetting__mdt(RelatedSObjectType__c = 'Account', DeveloperName = 'EnableFeature');
      System.assertEquals(1, [SELECT COUNT() FROM ProductSetting__mdt]);
    }
}