Changing all the raw asserts to self.assert in tests

[surgan12]

As pointed out by @fmassa here in #1465. We could switch the existing asserts to the self.assert version of it.

This could be a simple first issue for people to start with.

[fmassa]

I would recommend sending small-sized PRs, changing a single file / a few hundred lines at a time, to make reviewing easier.

[ekagra-ranjan]

@PyExtreme this could also be a good starting point for you :)

[PyExtreme]

Hi @ekagra-ranjan , this issue has already been picked. Thanks for letting me about it. I have started working on #1375 and that also looks very interesting.

Thank you