TST: adding test cases for verifying correct values shown by pivot_table() #21378
BUG: Incorrect values shown by pivot_table() #21378

- [x] closes #21378
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Just added a new test to verify the included patch in `master` branch
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21393?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@6c71c45`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21393/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/21393?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #21393   +/-   ##
=========================================
  Coverage          ?   91.89%           
=========================================
  Files             ?      153           
  Lines             ?    49604           
  Branches          ?        0           
=========================================
  Hits              ?    45586           
  Misses            ?     4018           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (?)` | |
| #single | `41.88% <ø> (?)` | |


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[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21393?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/21393?src=pr&el=footer). Last update [6c71c45...355aea3](https://codecov.io/gh/pandas-dev/pandas/pull/21393?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @gfyoung  thanks! you may now close the issue after the merge :+1:
 Hello @uds5501! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on June 15, 2018 at 17:32 Hours UTC @jreback  Done the changes. Any other improvement you'd like? @jreback fixed the errors in the test. Any other improvement required? thanks @uds5501 