Fix Web Client custom iterator

[smaeda-ks]

Summary

For Web Client, since SlackResponse class overrides an initial response data when iterating through the response object, it only returns the last fetched response data when it's iterated twice.

import slack

client = slack.WebClient(token='redacted')
response = client.channels_list(limit=50)

print('#### 1st iteration ####')

for i in response:
    print(i['channels'][0]['id'])

print('#### 2nd iteration ####')

for i in response:
    print(i['channels'][0]['id'])

Actual result

#### 1st iteration ####
C9A81JQQ4
CB2LQDJTB
CB34D9SQ3
CB3BF4953
CB48SJH1V
#### 2nd iteration ####
CB48SJH1V

Expected result

#### 1st iteration ####
C9A81JQQ4
CB2LQDJTB
CB34D9SQ3
CB3BF4953
CB48SJH1V
#### 2nd iteration ####
C9A81JQQ4
CB2LQDJTB
CB34D9SQ3
CB3BF4953
CB48SJH1V

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #521 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #521      +/-   ##
==========================================
+ Coverage   68.89%   68.92%   +0.03%     
==========================================
  Files          15       15              
  Lines        1707     1709       +2     
  Branches       96       96              
==========================================
+ Hits         1176     1178       +2     
  Misses        508      508              
  Partials       23       23

Impacted Files	Coverage Δ
slack/web/slack_response.py	97.77% <100%> (+0.1%)	⬆️

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[seratch]

I have tried to reproduce your situation but I can't.

[smaeda-ks]

@seratch Thanks, how did you test it? FYI, I tested it on my private workspace where there are over 200+ channels (and that's why I set limit=50 sorry if that was not obvious for you).

$ pip list | grep slackclient
slackclient   2.2.0

$ python --version
Python 3.7.3

[smaeda-ks]

Let me know if you need more clarification here. I'm pretty sure it's reproducible as long as you set the limit parameter value less than the total number of channels you're testing on.

[seratch]

set the limit parameter value less than the total number of channels

Thanks, I managed to reproduce it.

[seratch]

I confirmed that your fix addresses the issue by running it towards actual Slack APIs.

I wrote a unit test for this PR. Would you consider merging smaeda-ks#1 (or feel free to modify it as you like)? Then, I'll give 👍 to this PR.

[smaeda-ks]

@seratch Thanks for your help! Merged the PR to my forked branch so feel free to merge this PR accordingly.

[seratch]

@RodneyU215 I believe this one is ready to merge. Could you review this change when you have time?

[RodneyU215]

@smaeda-ks Thank you for the PR and thank you @seratch for adding in some tests. Super helpful fix. Looks good!