tests(model): add test coverage for model

[codecov-io]

Current coverage is 58.19% (diff: 100%)

Merging #276 into master will increase coverage by 11.79%

@@             master       #276   diff @@
==========================================
  Files             3          4     +1   
  Lines           306        311     +5   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits            142        181    +39   
+ Misses          160        121    -39   
- Partials          4          9     +5   

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[ultimateboy]

Before:

ok      github.com/deis/router/model    0.056s  coverage: 5.9% of statements
?       github.com/deis/router/utils    [no test files]

After:

ok      github.com/deis/router/model    0.070s  coverage: 29.4% of statements
ok      github.com/deis/router/utils    0.006s  coverage: 100.0% of statements

[krancour]

Awesome work on this!