TST: assert_dict_equal to check input type
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`

`assert_dict_equal` now checks input is `dict` instance. Fixed some tests which passes `Series` to it.

lgtm, merge on pass.
 thanks @sinhrks 

I added a couple of unrelated fixes to correct some numpy warnings.
