Add a unittests-nodisp environment.

.travis.yml

@@ -21,6 +21,7 @@ install:
 
 script:
     - xvfb-run -s "-screen 0 640x480x16" tox -e py34,py34-integration
+    - tox -e unittests-nodisp
     - tox -e misc
     - tox -e pep257
     - tox -e pyflakes

tox.ini

@@ -62,6 +62,15 @@ commands =
     {envpython} scripts/dev/freeze_tests.py build_exe -b {envdir}/build
     {envdir}/build/run-frozen-tests --strict -rfEsw {posargs}
 
+[testenv:unittests-nodisp]
+basepython = python3
+passenv = {[testenv]passenv}
+deps = {[testenv]deps}
+setenv = DISPLAY=
+commands =
+    {envpython} scripts/link_pyqt.py --tox {envdir}
+    {envpython} -m py.test --strict -rfEsw -m 'not integration' {posargs:tests}
+
 [testenv:misc]
 basepython = python3
 # For global .gitignore files