Add predicate tests

[hjl99]

Closes #172

[codecov-io]

Codecov Report

Merging #182 into master will increase coverage by 0.82%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #182      +/-   ##
============================================
+ Coverage     41.91%   42.73%   +0.82%     
- Complexity      762      790      +28     
============================================
  Files           134      134              
  Lines          3519     3519              
  Branches        483      483              
============================================
+ Hits           1475     1504      +29     
+ Misses         1872     1839      -33     
- Partials        172      176       +4     

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/chopchop/model/attributes/ExpiryDate.java	73.68% <0.00%> (ø)	8.00% <0.00%> (+2.00%)
...attributes/ExpiryDateMatchesKeywordsPredicate.java	77.77% <0.00%> (+77.77%)	7.00% <0.00%> (+7.00%)
...model/attributes/TagContainsKeywordsPredicate.java	84.61% <0.00%> (+84.61%)	9.00% <0.00%> (+9.00%)
...tributes/IngredientsContainsKeywordsPredicate.java	100.00% <0.00%> (+100.00%)	10.00% <0.00%> (+10.00%)

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[zhiayang]

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