Added test class for DummyWarning

[kgevorkyan]

What's done:

• Added test class for DummyWarning, which shows the general form of how to test your rule
• Add newline in guide-chapter-1, since table wasn't displayed

[codecov]

Codecov Report

Merging #810 (ae26311) into master (ee33cfd) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #810   +/-   ##
=========================================
  Coverage     80.95%   80.95%           
  Complexity     2248     2248           
=========================================
  Files            99       99           
  Lines          5738     5738           
  Branches       1783     1783           
=========================================
  Hits           4645     4645           
  Misses          286      286           
  Partials        807      807           

Flag	Coverage Δ	Complexity Δ
unittests	80.95% <ø> (ø)	0.00 <ø> (ø)

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[orchestr7]

lgtm, should be useful for newcomers.
I guess you can also write a small instruction in our readme of how to work with DummyWarning for your experiments

[petertrr]

You can run mvn diktat:fix@diktat to fix code style issues. Also, don't forget to select 'squash and merge'.