format_datetime: using 'S...S' format is incorrect

[shubh1m]

Fixes #350

[akx]

This is missing test cases.

You would need to prove that the earlier behavior is wrong and that this patch fixes it. :)

[shubh1m]

@akx Oh thanks!! I will see to it. 😄

[codecov-io]

Current coverage is 89.66%

Merging #353 into master will not affect coverage as of 2f9c97c

@@            master    #353   diff @@
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  Files           23      23       
  Stmts         3794    3794       
  Branches         0       0       
  Methods          0       0       
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  Hit           3402    3402       
  Partial          0       0       
  Missed         392     392       

Review entire Coverage Diff as of 2f9c97c

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[akx]

Hey @iamshubh22, okay, so now you have a test case, but I'd still like to see some sort of reasoning (maybe in the form of a reference to the particular piece of specification?) that explains why this new behavior is correct :)

In addition, a couple more test cases wouldn't go amiss, explaining the different cases that the newly implemented behavior covers.

[akx]

The docstring for a function needs to be before the code, not after. :)