Add test for rename() when oldPath and newPath are the same

[VictorKubrak]

I found out that existing tests do not test this case. Function should not rename the file, then it returns success status. I would like to add this test myself.

[humphd]

OK @VictorKubrak, go for it.

[Pooch11]

By the looks of things in other issues - the goal is to move closer to IEEE standard. Consider looking at The Open Group this will show what the expected behaviour of this function is. I did not see any restrictions on renaming a file with the same name. Nevertheless - its probably a missing test!