Migrate to AssertJ for assertions (#122)

[vpondala]

Converted most of the assertions to AssertJ assertions.

[vpondala]

The value %20 is causing issue with comparision of strings due to this: http://joel-costigliola.github.io/assertj/core-8/api/org/assertj/core/api/AbstractStringAssert.html#isEqualTo-java.lang.String-java.lang.Object...-

Let me find if something can be done to avoid this issue.

[codecov[bot]]

Codecov Report

Merging #163 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #163   +/-   ##
=========================================
  Coverage     90.47%   90.47%           
  Complexity      128      128           
=========================================
  Files            42       42           
  Lines           399      399           
  Branches         45       45           
=========================================
  Hits            361      361           
  Misses           14       14           
  Partials         24       24

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[rybalkinsd]

@gokulchandra would you mind to review this?

[rybalkinsd]

Thanks @vpondala ! Just merge it and change seems perfect