Tests for queue and stack updated

[HarsheetKakar]

References to other Issues or PRs or Relevant literature

Fixes #154

Brief description of what is fixed or changed

Other comments

please check if the changes in init.py are acceptable

[codecov]

Codecov Report

Merging #163 into master will increase coverage by 0.003%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master      #163       +/-   ##
=============================================
+ Coverage   98.325%   98.328%   +0.003%     
=============================================
  Files           21        21               
  Lines         1612      1615        +3     
=============================================
+ Hits          1585      1588        +3     
  Misses          27        27               

Impacted Files	Coverage Δ
...datastructs/miscellaneous_data_structures/stack.py	100.000% <100.000%> (ø)

[czgdp1807]

Test both the implementations but use the interface classes Queue and Stack to test. Implementation classes shouldn't be accessed.