diff --git a/.travis.yml b/.travis.yml
index 8e76d66..7f7bcc5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,27 +1,55 @@
 ---
 dist: xenial
 language: python
+env:
+  global:
+    - LSR_NEED_PYLINTERS="/^linux-system-roles\/(network|selinux|storage)$/"
 matrix:
   include:
     - python: 2.6
       dist: trusty
+      # Use LSRENV to save the unique value (here the desired Python
+      # interpreter version) to distinguish between Travis jobs. This can be
+      # usefull if some role wish to perform a specific action depending on the
+      # job environment:
+      env: LSRENV=2.6
+      # Skip the jobs where only Python linters are run if the role does not
+      # contain any Python code:
+      if: repo =~ env(LSR_NEED_PYLINTERS)
     - python: 2.7
+      env: LSRENV=2.7
+      if: repo =~ env(LSR_NEED_PYLINTERS)
     - python: 3.5
-      env: aptpkgs=python3-selinux
+      env: LSRENV=3.5
+      # Under 3.5, we run Molecule
     - python: 3.6
+      env: LSRENV=3.6
+      if: repo =~ env(LSR_NEED_PYLINTERS)
     - python: 3.7
+      env: LSRENV=3.7
+      if: repo =~ env(LSR_NEED_PYLINTERS)
     - python: 3.7-dev
+      env: LSRENV=3.7-dev
+      if: repo =~ env(LSR_NEED_PYLINTERS)
     - python: 3.8-dev
-    # - python: nightly
+      env: LSRENV=3.8-dev
+      if: repo =~ env(LSR_NEED_PYLINTERS)
+    #- python: nightly
+    #  env: LSRENV=nightly
+    #  if: repo =~ env(LSR_NEED_PYLINTERS)
 
 services:
   - docker
 
 before_install:
-  - if [ -n "${aptpkgs}" ]; then sudo apt-get install -y python3-selinux; fi
+  # In .travis/before_install.sh can be commands that install packages specific
+  # for the concrette role, or set specific environment variables. To decide
+  # what to set or install in which environment, the value of LSRENV should be
+  # helpfull:
+  - if [ -f .travis/before_install.sh ]; then .travis/before_install.sh; fi
 
 install:
-  - pip install tox tox-travis
+  - pip install molecule docker tox tox-travis
 
 script:
   - tox
diff --git a/.travis/before_install.sh b/.travis/before_install.sh
new file mode 100755
index 0000000..23de95b
--- /dev/null
+++ b/.travis/before_install.sh
@@ -0,0 +1,17 @@
+#!/bin/bash
+
+if [ x${LSRENV} = x2.7 ]; then
+  LSR_PYLINT_DIRS='library/network_connections.py module_utils/network_lsr tests/unit/test_network_connections.py'
+fi
+
+if [ x${LSRENV} = x3.5 ]; then
+  LSR_MOLECULE_DEPS='-rmolecule_requirements.txt'
+
+  sudo apt-get install -y python3-selinux
+fi
+
+if [ x${LSRENV} = x3.6 ]; then
+  LSR_TEXTRA_DEPS='PyYAML'
+  LSR_TEXTRA_DIR='tests'
+  LSR_TEXTRA_CMD='./ensure_non_running_provider.py'
+fi
diff --git a/molecule_requirements.txt b/molecule_requirements.txt
new file mode 100644
index 0000000..20a040b
--- /dev/null
+++ b/molecule_requirements.txt
@@ -0,0 +1,2 @@
+jmespath
+git+https://github.com/tyll/selinux-pypi-shim@fulllocation
diff --git a/tox.ini b/tox.ini
index 604c295..8bb7840 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,23 +1,15 @@
 [tox]
-envlist = black, flake8, pylint, py{26,27,36,37}, ensure_non_running_provider
 skipsdist = true
-skip_missing_interpreters = True
+skip_missing_interpreters = true
 
 [testenv]
 basepython = python3
+# List common dependencies for Python interpreters here:
 deps =
     py{26,27,36,37,38}: pytest-cov
     py{27,36,37,38}: pytest>=3.5.1
     py{26,27}: mock
     py26: pytest
-    molecule_{lint,syntax,test}: docker
-    molecule_{lint,syntax,test}: jmespath
-    molecule_{lint,syntax,test}: molecule
-    # The selinux pypi shim does not work with Ubuntu (as used by Travis), yet.
-    # Therefore use a fork with Ubuntu support. This can be changed once the
-    # update is available on PyPi.
-    # molecule_{lint,syntax,test}: selinux
-    molecule_{lint,syntax,test}: git+https://github.com/tyll/selinux-pypi-shim@fulllocation
 
 [base]
 passenv = *
@@ -29,25 +21,28 @@ covtarget = {toxinidir}/library --cov {toxinidir}/module_utils
 pytesttarget = .
 
 [testenv:black]
-deps = black
-
-commands = black --check --diff --include "^[^.].*\.py$" .
+deps =
+    black
+commands =
+    black --check --diff --include "^[^.].*\.py$" --exclude "/(\.[^.].*|tests/roles)/" .
 
 [testenv:py26]
-install_command = pip install {opts} {packages}
-list_dependencies_command = pip freeze
+install_command =
+    pip install {opts} {packages}
+list_dependencies_command =
+    pip freeze
 basepython = python2.6
 passenv = {[base]passenv}
 setenv =
     {[base]setenv}
 changedir = {[base]changedir}
 commands =
-    pytest \
-        --durations=5 \
-        --cov={[base]covtarget} \
-        --cov-report=html:htmlcov-py26 --cov-report=term \
-        {posargs} \
-        {[base]pytesttarget}
+    pytest --durations=5 \
+           --cov={[base]covtarget} \
+           --cov-report=html:htmlcov-py26 \
+           --cov-report=term \
+           {posargs} \
+           {[base]pytesttarget}
 
 [testenv:py27]
 basepython = python2.7
@@ -56,12 +51,12 @@ setenv =
     {[base]setenv}
 changedir = {[base]changedir}
 commands =
-    pytest \
-        --durations=5 \
-        --cov={[base]covtarget} \
-        --cov-report=html:htmlcov-py27 --cov-report=term \
-        {posargs} \
-        {[base]pytesttarget}
+    pytest --durations=5 \
+           --cov={[base]covtarget} \
+           --cov-report=html:htmlcov-py27 \
+           --cov-report=term \
+           {posargs} \
+           {[base]pytesttarget}
 
 [testenv:py36]
 basepython = python3.6
@@ -70,12 +65,12 @@ setenv =
     {[base]setenv}
 changedir = {[base]changedir}
 commands =
-    pytest \
-        --durations=5 \
-        --cov={[base]covtarget} \
-        --cov-report=html:htmlcov-py36 --cov-report=term \
-        {posargs} \
-        {[base]pytesttarget}
+    pytest --durations=5 \
+           --cov={[base]covtarget} \
+           --cov-report=html:htmlcov-py36 \
+           --cov-report=term \
+           {posargs} \
+           {[base]pytesttarget}
 
 [testenv:py37]
 basepython = python3.7
@@ -84,27 +79,33 @@ setenv =
     {[base]setenv}
 changedir = {[base]changedir}
 commands =
-    pytest \
-        --durations=5 \
-        --cov={[base]covtarget} \
-        --cov-report=html:htmlcov-py37 --cov-report=term \
-        {posargs} \
-        {[base]pytesttarget}
+    pytest --durations=5 \
+           --cov={[base]covtarget} \
+           --cov-report=html:htmlcov-py37
+           --cov-report=term \
+           {posargs} \
+           {[base]pytesttarget}
 
 [testenv:py38]
+basepython = python3.8
 passenv = {[base]passenv}
 setenv =
     {[base]setenv}
 changedir = {[base]changedir}
-basepython = python3.8
 commands =
-    pytest \
-        --durations=5 \
-        --cov={[base]covtarget} \
-        --cov-report=html:htmlcov-py38 --cov-report=term \
-        {posargs} \
-        {[base]pytesttarget}
+    pytest --durations=5 \
+           --cov={[base]covtarget} \
+           --cov-report=html:htmlcov-py38 \
+           --cov-report=term \
+           {posargs} \
+           {[base]pytesttarget}
 
+# Custom role settings may set LSR_PYLINT_DIRS environment variable if there is
+# a reason to have other than default directories (library/ module_utils/ and
+# tests/). For example, network role should have this set like
+#
+#   LSR_PYLINT_DIRS="library/network_connections.py module_utils/network_lsr tests/unit/test_network_connections.py"
+#
 [testenv:pylint]
 basepython = python2.7
 setenv =
@@ -113,21 +114,17 @@ deps =
     pylint>=1.8.4
     ansible
 commands =
-    pylint \
-        --errors-only \
-        {posargs} \
-        library/network_connections.py \
-        module_utils/network_lsr \
-        tests/unit/test_network_connections.py
+    pylint --errors-only \
+           {posargs} \
+           {env:LSR_PYLINT_DIRS:library module_utils tests}
 
 [testenv:flake8]
 basepython = python2.7
 deps =
     flake8>=3.5
 whitelist_externals = flake8
-commands=
-    flake8 --statistics {posargs} \
-        .
+commands =
+    flake8 --statistics {posargs} .
 
 [testenv:coveralls]
 basepython = python2.7
@@ -138,29 +135,83 @@ changedir = {[base]changedir}
 commands =
     coveralls
 
-[testenv:ensure_non_running_provider]
+# Here we provide a way how a role can add its custom command to be run. Such
+# extra command is run at the end of each testenv run and is driven by
+# environment variables. Involved environment variables are:
+#
+#   LSR_TEXTRA_DEPS
+#     - contains dependency needed by commands to run smoothly; if more than
+#       one dependency is needed, use external file together with '-r' option
+#       (see PEP 508)
+#
+#   LSR_TEXTRA_DIR
+#     - directory to which to cd
+#
+#   LSR_TEXTRA_CMD
+#     - custom command to be run
+#
+# Example: `network` system role need to run `./tests/ensure_non_running_provider.py`
+#          to check for the existence of `*_provider.yml` playbooks. The script
+#          is run in Python 3.6.
+#
+#          To make this possible, we add to `.travis/before_install.sh` a snippet:
+#
+#              if [ x${LSRENV} = x3.6 ]; then
+#                LSR_TEXTRA_DEPS='PyYAML'
+#                LSR_TEXTRA_DIR='tests'
+#                LSR_TEXTRA_CMD='./ensure_non_running_provider.py'
+#              fi
+#
+[testenv:extra]
+passenv = *
 deps =
-    PyYAML
-changedir = {toxinidir}/tests
-commands = {toxinidir}/tests/ensure_non_running_provider.py
+    {env:LSR_TEXTRA_DEPS}
+changedir = {toxinidir}/{env:LSR_TEXTRA_DIR:.}
+commands =
+    {env:LSR_TEXTRA_CMD:python --version}
+
+# LSR_MOLECULE_DEPS may contain aditional Molecule dependencies. For example,
+# in `network` system role, LSR_MOLECULE_DEPS can be set as
+#
+#   LSR_MOLECULE_DEPS='-rmolecule_requirements.txt'
+#
+# where `molecule_requirements.txt` contains two lines:
+#
+#   jmespath
+#   git+https://github.com/tyll/selinux-pypi-shim@fulllocation
+#
+[molecule]
+deps =
+    docker
+    molecule
+    {env:LSR_MOLECULE_DEPS}
 
 [testenv:molecule_lint]
+deps =
+    {[molecule]deps}
 commands_pre =
     molecule --version
     ansible --version
-commands = molecule {posargs} lint
+commands =
+    molecule {posargs} lint
 
 [testenv:molecule_syntax]
-commands = molecule {posargs} syntax
+deps =
+    {[molecule]deps}
+commands =
+    molecule {posargs} syntax
 
 [testenv:molecule_test]
-commands = molecule {posargs} test
+deps =
+    {[molecule]deps}
+commands =
+    molecule {posargs} test
 
 [pytest]
 addopts = -rxs
 
 [flake8]
-show_source = True
+show_source = true
 max-line-length = 88
 ignore = E402,W503
 
@@ -173,9 +224,9 @@ max-line-length = 88
 
 [travis]
 python =
-  2.6: py26
-  2.7: py27,coveralls,flake8,pylint
-  3.5: molecule_lint,molecule_syntax,molecule_test
-  3.6: py36,black,ensure_non_running_provider
-  3.7: py37
-  3.8: py38
+  2.6: py26,extra
+  2.7: py27,coveralls,flake8,pylint,extra
+  3.5: molecule_lint,molecule_syntax,molecule_test,extra
+  3.6: py36,black,extra
+  3.7: py37,extra
+  3.8: py38,extra