TST: Fix makeObjectSeries data as object type
State: closed

- [x] closes #28378 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry


Labels:
name: Testing
description: pandas testing functions or related to the test suite

Comments:
Cool this looks good. Any chance you looked at where this was ultimately used? Would be nice to clean up any casting that this required in the past
Umm, there is no casting about this.

One thing that I can doubt is usage on `test_objarr_add_invalid`. Because it tested about `add` and `sub` operation on object that made by `datetime64[ns]`.
It is at `pandas/tests/arithmetic/test_object.py L144`.

Other things are used just representing a `series` made by `object` as I summarized at #28378.

Can you tell me more details about what should I do?

And should I add an entry at whatsnew on v1.0?
> One thing that I can doubt is usage on `test_objarr_add_invalid`. Because it tested about `add` and `sub` operation on object that made by `datetime64[ns]`.
> It is at `pandas/tests/arithmetic/test_object.py L144`.

Yea that's a great find - thanks for being thorough. Can you see where that was introduced to see what the intention was? The fact that it blanket catches an `Exception` is a little bit of a red flag as to the intent.

Also looking these over I'm surprised that all of the `makeABCSeries` methods don't actually make a series of dtype `ABC`, but instead just contain an index of dtype `ABC`. Do you have any thoughts on how those methods are comprehensively used?
> Can you see where that was introduced to see what the intention was? 

Although I can't find origin of `test_objarr_add_invalid`, but it's intention was raising error on numerical operator about `datetime64[ns]` like object. Here's my reference(https://github.com/pandas-dev/pandas/commit/91ee418fe8ebe2951599eeb49159379c5200c029). I can't find more deeply because file was deleted.(`pandas/tests/test_series.py`)
https://github.com/pandas-dev/pandas/blob/91ee418fe8ebe2951599eeb49159379c5200c029/pandas/tests/series/test_operators.py#L187-L195
So, test would be modified as `datetime64[ns]` converted to base object.

> Also looking these over I'm surprised that all of the `makeABCSeries` methods don't actually make a series of dtype `ABC`, but instead just contain an index of dtype `ABC`. 

Yes, only `makeObjectSeries` returns a series that contains `dtype=object`... It is so weird. I think `makeObjectSeries` do correct job and other things are not. I think every `makeABCSeries` should return `dtype=ABC` with default index. What do you expect as exact result of `makeABCSeries`? 

> Do you have any thoughts on how those methods are comprehensively used?

About that, it's too hard question to me :)
> I think `makeObjectSeries` do correct job and other things are not. I think every `makeABCSeries` should return `dtype=ABC` with default index.

Yea that seems logical to me though doesn't appear to be the case. cc @jreback in case of any historical knowledge as to why things are that way
thanks @jmg7173 

yeah we likely have enough testing already in place.