add message tests.

[zingimmick]

No description provided.

[codecov]

Codecov Report

Merging #2 into master will increase coverage by 2.76%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master       #2      +/-   ##
============================================
+ Coverage     86.22%   88.98%   +2.76%     
- Complexity      102      103       +1     
============================================
  Files            17       17              
  Lines           225      227       +2     
============================================
+ Hits            194      202       +8     
+ Misses           31       25       -6     

Impacted Files	Coverage Δ	Complexity Δ
src/Message.php	100.00% <100.00%> (+15.38%)	22.00 <9.00> (+1.00)

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