@isTest
private class CheckChatterPostsTest {
    @isTest
    static void testError() {
        FeedItem f = new FeedItem(
            Type = 'TextPost',
            ParentId = Userinfo.getUserId(),
            Body = 'Text'
        );
        Database.SaveResult[] lsr = Database.insert(new FeedItem[] {f}, false);
        for (Integer sIdx = 0; sIdx < lsr.size(); sIdx++) {
            Database.SaveResult sr = lsr[sIdx];
            System.assertEquals(false, sr.isSuccess());
            System.assertEquals(System.Label.Error_ChatterPostToMyFollowers, sr.getErrors()[0].getMessage());
        }
    }
}