"Who tested it." or "Who it tested"?

[Nightmare85]

Hello,
A while ago I asked a friend but we both were not very sure.
It's about the sentence:
Who tested it.

Important: It's not a question!

In some other forums I created a big list that contained plenty of information.
Some guys helped me and I wrote a credits list.
As an explanation (what the credits list contain) I wrote:

author of the explanation, where the information came from, who tested it, and so on.

First I wrote: "Who it tested.", but then I decided to change it.

The main question:
Which one is correct?
Who tested it.
or
Who it tested.
:?:

P.S: I would be very thankful if you could explain it :up:

I definitely know that:
The guy who tested it is now my friend. is correct
but
The guy who it tested is now my friend. is wrong

Is it the same rule as for the other example?

Cheers!

 

[Linguist__]

(Not a teacher)

I would say it is the same rule.

'... who tested it' means that the 'who' did the testing on the 'it'.

'... who it tested' means that the 'it' did the testing on the 'who'.

 

[Searching for language]

(Not a teacher)

I would say it is the same rule.

'... who tested it' means that the 'who' did the testing on the 'it'.

'... who it tested' means that the 'it' did the testing on the 'who'.

So, if "it" did the testing, then it should be "whom it tested"

As in, "The exercise between right and wrong was very difficult, and whom it tested had a problem deciding the correct answer."

I am not a teacher.