REF/TST: Add more pytest idiom to mi indexing tests 
State: closed

- [n/a ] follow on from #23912
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [n/a ] whatsnew entry

for this pass:

- the Test classes have been removed.

- `catch_warnings`  used for the `.ix` deprecation replaced with `@pytest.mark.filterwarnings("ignore:\\n.ix:DeprecationWarning")` at test level.


Labels:
name: Refactor
description: Internal refactoring of code
name: Testing
description: pandas testing functions or related to the test suite
name: MultiIndex

Comments:
Hello @simonjayhawkins! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_getitem.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_getitem.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_iloc.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_iloc.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_ix.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_ix.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_loc.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_loc.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_multiindex.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_multiindex.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_panel.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_panel.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_partial.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_partial.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_set_ops.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_set_ops.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_setitem.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_setitem.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_slice.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_slice.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_sorted.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_sorted.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexing/multiindex/test_xs.py`](https://github.com/simonjayhawkins/pandas/blob/c97de72fecb37c1e0648377d054a346a912dd00e/pandas/tests/indexing/multiindex/test_xs.py) !


# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=h1) Report
> Merging [#24040](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b45eb265dd88648fb02ebb0fdcfb168364ab664e?src=pr&el=desc) will **increase** coverage by `49.88%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24040/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #24040       +/-   ##
===========================================
+ Coverage   42.46%   92.35%   +49.88%     
===========================================
  Files         161      161               
  Lines       51557    51557               
===========================================
+ Hits        21892    47613    +25721     
+ Misses      29665     3944    -25721
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.75% <ø> (?)` | |
| #single | `42.46% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/computation/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vcHl0YWJsZXMucHk=) | `92.37% <0%> (+0.3%)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.3% <0%> (+0.92%)` | :arrow_up: |
| [pandas/util/\_test\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3Rlc3RfZGVjb3JhdG9ycy5weQ==) | `93.24% <0%> (+4.05%)` | :arrow_up: |
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `58.36% <0%> (+8.17%)` | :arrow_up: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `99.24% <0%> (+9.84%)` | :arrow_up: |
| [pandas/core/reshape/util.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS91dGlsLnB5) | `100% <0%> (+11.53%)` | :arrow_up: |
| [pandas/compat/numpy/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9udW1weS9fX2luaXRfXy5weQ==) | `92.85% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/computation/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vY29tbW9uLnB5) | `85.71% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBpLnB5) | `100% <0%> (+14.81%)` | :arrow_up: |
| [pandas/core/indexes/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9hcGkucHk=) | `99% <0%> (+14.85%)` | :arrow_up: |
| ... and [119 more](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=footer). Last update [b45eb26...c97de72](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=h1) Report
> Merging [#24040](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b45eb265dd88648fb02ebb0fdcfb168364ab664e?src=pr&el=desc) will **increase** coverage by `49.88%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24040/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #24040       +/-   ##
===========================================
+ Coverage   42.46%   92.35%   +49.88%     
===========================================
  Files         161      161               
  Lines       51557    51557               
===========================================
+ Hits        21892    47613    +25721     
+ Misses      29665     3944    -25721
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.75% <ø> (?)` | |
| #single | `42.46% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/computation/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vcHl0YWJsZXMucHk=) | `92.37% <0%> (+0.3%)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.3% <0%> (+0.92%)` | :arrow_up: |
| [pandas/util/\_test\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3Rlc3RfZGVjb3JhdG9ycy5weQ==) | `93.24% <0%> (+4.05%)` | :arrow_up: |
| [pandas/compat/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fX2luaXRfXy5weQ==) | `58.36% <0%> (+8.17%)` | :arrow_up: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `99.24% <0%> (+9.84%)` | :arrow_up: |
| [pandas/core/reshape/util.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS91dGlsLnB5) | `100% <0%> (+11.53%)` | :arrow_up: |
| [pandas/compat/numpy/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9udW1weS9fX2luaXRfXy5weQ==) | `92.85% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/computation/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vY29tbW9uLnB5) | `85.71% <0%> (+14.28%)` | :arrow_up: |
| [pandas/core/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBpLnB5) | `100% <0%> (+14.81%)` | :arrow_up: |
| [pandas/core/indexes/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9hcGkucHk=) | `99% <0%> (+14.85%)` | :arrow_up: |
| ... and [119 more](https://codecov.io/gh/pandas-dev/pandas/pull/24040/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=footer). Last update [b45eb26...c97de72](https://codecov.io/gh/pandas-dev/pandas/pull/24040?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

@gfyoung  thanks for the review. breaking down the PR is not a problem. would your preference be to split by activity, by file or perhaps limit the number of files in the PR?
@simonjayhawkins here i think you can split by files. e.g. try to limit the amount that requires review in any 1 PR. Also if you have a PR which simply moves things, those should be independent to making actual changes.
> here i think you can split by files.

I second @jreback on this.