Increasing coverage on few components in preparation for 0.6.x refactors

Components:

 * view engines
 * mojito.js
 * action-context

```
----------------------------------------+-----------+-----------+-----------+-----------+
File                                    |   % Stmts |% Branches |   % Funcs |   % Lines |
----------------------------------------+-----------+-----------+-----------+-----------+
      action-context.common.js          |     89.68 |     80.17 |        85 |     89.68 |
      hb.server.js                      |     90.77 |     86.49 |     86.67 |     90.77 |
      hb.client.js                      |     88.33 |     86.49 |        75 |     88.33 |
      mojito.js                         |      90.5 |     74.11 |        84 |      90.5 |
----------------------------------------+-----------+-----------+-----------+-----------+
```