Added pytest-raises

Converted test_units to use parametrize

Some hacking of test_distances to use pytest features

Completed moving test_distances to pytest style

rewrote test_transformations into pytest style

.travis.yml

@@ -31,7 +31,7 @@ env:
     - MAIN_CMD="pytest ${PYTEST_LIST} ${PYTEST_FLAGS}; python ./testsuite/MDAnalysisTests/mda_nosetests ${NOSE_TEST_LIST} ${NOSE_FLAGS}"
     - SETUP_CMD=""
     - BUILD_CMD="pip install -v package/ && pip install testsuite/"
-    - CONDA_DEPENDENCIES="mmtf-python nose=1.3.7 mock six biopython networkx cython joblib nose-timer pytest=3.1.2 pytest-cov=2.5.1"
+    - CONDA_DEPENDENCIES="mmtf-python nose=1.3.7 mock six biopython networkx cython joblib nose-timer pytest=3.1.2 pytest-cov=2.5.1 pytest-raises"
     - CONDA_ALL_DEPENDENCIES="mmtf-python nose=1.3.7 mock six biopython networkx cython joblib nose-timer matplotlib netcdf4 scikit-learn scipy seaborn coveralls clustalw=2.1 pytest=3.1.2 pytest-cov=2.5.1"
     # Install griddataformats from PIP so that scipy is only installed in the full build (#1147)
     - PIP_DEPENDENCIES='griddataformats'