One wonders here if there isn’t an of missing in the phrase “testified these things”. We note that the Book of Mormon text has 16 instances of “to testify of things”, including three in this same chapter of Helaman:
Nonetheless, there is some evidence for “to testify things”. In the Book of Mormon text, we have one more example without the of:
One could argue, of course, that this example is not quite the same since there is an intervening prepositional phrase, “unto this people”, between the verb testify and the direct object (“the things which have been spoken by our fathers”).
Turning to the King James Bible, we can find examples of all these types, with and without the of, including one case where there is an intervening prepositional phrase:
The example in Revelation 22:16 parallels Alma 5:44 while the one in Revelation 22:20 parallels Helaman 8:19. The critical text will therefore maintain the two Book of Mormon occurrences of “to testify things” without the preposition of.
Summary: Maintain the occurrence in the text of “to testify things” (that is, without the expected preposition of ), with one example in Alma 5:44 and another here in Helaman 8:19; usage in the King James Bible supports this occasional lack of of in the Book of Mormon text.