Quality tests for public API

[czgdp1807]

References to other Issues or PRs or Relevant literature

Closes #254

Brief description of what is fixed or changed

Tests that if a method which is must for child class is there in it rather than being accessed from parent class. Uses MRO to find out where the required method is.

Other comments

[codecov]

Codecov Report

Merging #255 into master will increase coverage by 0.227%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master      #255       +/-   ##
=============================================
+ Coverage   98.546%   98.774%   +0.227%     
=============================================
  Files           24        23        -1     
  Lines         2202      2285       +83     
=============================================
+ Hits          2170      2257       +87     
+ Misses          32        28        -4     

Impacted Files	Coverage Δ
pydatastructs/graphs/adjacency_list.py	100.000% <100.000%> (ø)
pydatastructs/graphs/adjacency_matrix.py	100.000% <100.000%> (ø)
pydatastructs/linear_data_structures/arrays.py	100.000% <100.000%> (ø)
...datastructs/linear_data_structures/linked_lists.py	99.596% <100.000%> (-0.018%)	⬇️
...ts/miscellaneous_data_structures/binomial_trees.py	100.000% <100.000%> (ø)
...ucts/miscellaneous_data_structures/disjoint_set.py	100.000% <100.000%> (ø)
...datastructs/miscellaneous_data_structures/queue.py	100.000% <100.000%> (ø)
...datastructs/miscellaneous_data_structures/stack.py	100.000% <100.000%> (ø)
pydatastructs/trees/binary_trees.py	97.094% <100.000%> (+0.060%)	⬆️
pydatastructs/trees/heaps.py	97.927% <100.000%> (+0.089%)	⬆️
... and 6 more