Add a test example for calling getWork() on a missing document returning a 404

[bmquinn]

Test coverage up to 100% 🎉 :

-----------------|---------|----------|---------|---------|-------------------
File             | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------------|---------|----------|---------|---------|-------------------
All files        |     100 |      100 |     100 |     100 |                   
 api             |     100 |      100 |     100 |     100 |                   
  opensearch.js  |     100 |      100 |     100 |     100 |                   
 aws             |     100 |      100 |     100 |     100 |                   
  environment.js |     100 |      100 |     100 |     100 |                   
  fetch.js       |     100 |      100 |     100 |     100 |                   
-----------------|---------|----------|---------|---------|-------------------

[mbklein]

🎉