TST: change assertion messages in assert_frame_equal (#27023)
- [x] closes #27023
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Ouch, this is my first pandas PR, are all of these failing checks normal? The change is so tiny, I can't imagine what could have gone wrong. Ah shoot, I see that there are tests that fail now, which match on the assertion text that I changed.
I'll take a closer look at whether the discrepant tests make sense to be updated. I don't totally understand the `by_blocks` test though, so any insight would be appreciated.  > I don't totally understand the `by_blocks` test though, so any insight would be appreciated.

I *think* you are referring to the `test_frame_equal_block_mismatch` which is the one that is failing. This is *parametrized* with the `by_blocks` *fixture*, which basically means the test gets run twice (once where `by_blocks` is `True` and another time where it is `False`)

Haven't looked deep into the failure but hope the above helps If in the `if by_blocks:` block we change
```python
assert_frame_equal(...
   obj='{obj}.blocks'.format(obj=obj))
```
to just
```python
assert_frame_equal(...
   obj=obj)
```
the existing tests are happy. Note the original string is hard-coded `'DataFrame.blocks'`. What I'm not sure of yet is if it makes sense to remove the `.blocks` part of the string, or if the test cases should be updated. Or neither or something else.  I don't think `.blocks` needs to necessarily be appended as the original hard coding of `DataFrame.blocks` is arguably arbitrary to begin with # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=h1) Report
> Merging [#27068](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e9555159afd8caabc88b45ca6c06a16efe2f6afc?src=pr&el=desc) will **decrease** coverage by `50.17%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/27068/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #27068       +/-   ##
===========================================
- Coverage   92.04%   41.86%   -50.18%     
===========================================
  Files         180      180               
  Lines       50714    50714               
===========================================
- Hits        46679    21233    -25446     
- Misses       4035    29481    +25446
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.86% <100%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `51.05% <100%> (-39.79%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/gcs.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2djcy5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/s3.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3MzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.16%)` | :arrow_down: |
| ... and [133 more](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27068?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/27068?src=pr&el=footer). Last update [e955515...fc23941](https://codecov.io/gh/pandas-dev/pandas/pull/27068?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/27068?src=pr&el=h1) Report
> Merging [#27068](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e9555159afd8caabc88b45ca6c06a16efe2f6afc?src=pr&el=desc) will **decrease** coverage by `50.17%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/27068/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #27068       +/-   ##
===========================================
- Coverage   92.04%   41.86%   -50.18%     
===========================================
  Files         180      180               
  Lines       50714    50714               
===========================================
- Hits        46679    21233    -25446     
- Misses       4035    29481    +25446
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.86% <100%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `51.05% <100%> (-39.79%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/gcs.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2djcy5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/s3.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3MzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.16%)` | :arrow_down: |
| ... and [133 more](https://codecov.io/gh/pandas-dev/pandas/pull/27068/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27068?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/27068?src=pr&el=footer). Last update [e955515...fc23941](https://codecov.io/gh/pandas-dev/pandas/pull/27068?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 > Merging #27068 into master will decrease coverage by 50.17%

Ouch, I'm not not having much luck with this! I don't understand where that drop in coverage could be coming from. Does this mean there is more digging I should be doing? Don't worry about codecov it's sometimes spotty. Can you add a test in pandas/tests/util/test_assert_frame_equal.py that ensures this works correctly? I'm not sure if I went overboard in the test script, by adding parametrization to all of the existing tests. Let me know, and I'd be happy do revert and redo, as a new test or two. thanks @ajwood  > thanks @ajwood

My pleasure! @WillAyd thanks for the help :)