Refactor Python tests. (#3897)

* Deprecate nose tests.
* Format python tests.

tests/ci_build/Dockerfile.gpu

@@ -37,7 +37,7 @@ ENV CPP=/opt/rh/devtoolset-2/root/usr/bin/cpp
 
 # Install Python packages
 RUN \
-    pip install numpy nose scipy scikit-learn wheel
+    pip install numpy pytest scipy scikit-learn wheel
 
 ENV GOSU_VERSION 1.10
 

tests/ci_build/Dockerfile.release

@@ -15,8 +15,8 @@ ENV PATH=/opt/python/bin:$PATH
 
 # Install Python packages
 RUN \
-    conda install numpy scipy pandas matplotlib nose scikit-learn && \
-    pip install nose wheel auditwheel graphviz
+    conda install numpy scipy pandas matplotlib pytest scikit-learn && \
+    pip install pytest wheel auditwheel graphviz
 
 ENV GOSU_VERSION 1.10
 

tests/ci_build/test_gpu.sh

@@ -4,6 +4,5 @@ set -e
 cd python-package
 python setup.py install --user
 cd ..
-python -m nose -v --eval-attr='(not slow) and (not mgpu)' tests/python-gpu/
+pytest -v -s --fulltrace -m "(not mgpu) and (not slow)" tests/python-gpu
 ./testxgboost --gtest_filter=-*.MGPU_*
-

tests/ci_build/test_mgpu.sh

@@ -4,5 +4,5 @@ set -e
 cd python-package
 python setup.py install --user
 cd ..
-python -m nose -v --eval-attr='(not slow) and mgpu' tests/python-gpu/
+pytest -v -s --fulltrace -m "(not slow) and mgpu" tests/python-gpu
 ./testxgboost --gtest_filter=*.MGPU_*