TST: ujson tests are not being run
#### Code Sample, a copy-pastable example if possible

```
pytest pandas/tests/io/json/test_ujson.py 
=========================================================== test session starts ============================================================
platform darwin -- Python 3.6.1, pytest-3.0.7, py-1.4.33, pluggy-0.4.0
rootdir: /pandas_dev, inifile: setup.cfg
plugins: cov-2.3.1, xdist-1.16.0
collected 0 items 

======================================================= no tests ran in 0.21 seconds =======================================================
```
#### Problem description

likely related to the PyTest move.  Classes do not start with keyword **Test**

#### Expected Output

likely missing over 100 tests.