Test all modules (including underscores), and always doctest

.travis.yml

@@ -27,6 +27,7 @@ before_install:
     - sh -e /etc/init.d/xvfb start
     - export PYTHONWARNINGS="all"
     - export WHEELHOUSE="--no-index --find-links=http://travis-wheels.scikit-image.org/"
+    - export TEST_ARGS="--exe -v --all-modules --with-doctest"
     - sudo apt-get update
 
     - travis_retry tools/travis_setup.sh
@@ -46,7 +47,7 @@ install:
 
 script:
     - tools/header.py "Run all tests with minimum dependencies"
-    - nosetests --exe -v skimage
+    - nosetests $TEST_ARGS skimage
 
     - tools/header.py "Pep8 and Flake tests"
     - flake8 --exit-zero --exclude=test_*,six.py skimage doc/examples viewer_examples

tools/travis_test.sh

@@ -40,7 +40,6 @@ echo 'backend.qt4 : '$MPL_QT_API >> $MPL_DIR/matplotlibrc
 
 tools/header.py "Run tests with all dependencies"
 # run tests again with optional dependencies to get more coverage
-TEST_ARGS='--exe -v --with-doctest'
 if [[ $TRAVIS_PYTHON_VERSION == 3.3 ]]; then
     TEST_ARGS="$TEST_ARGS --with-cov --cover-package skimage"
 fi