Add unit tests for SearchEngine.search

Adds unit tests for the SearchEngine.search function, specifically
building on commit b4591df9e9af8052676fa2ad1bcbf0362ebe176f so we can
test the logic around the 'recent' argument.

Change-Id: Icbdde7afeecfa201f5554d0105fd54fd848b1335
Merge "Add unit tests for SearchEngine.search"