Refactor how test are run, add tests to exercise pytype (if installed) (#353)

.travis.yml

@@ -1,15 +1,18 @@
 sudo: false
 language: python
-python:
-  - "3.5"
-  # More versions later.
+
+matrix:
+  include:
+    - python: "3.5"
+      env: TEST_CMD="./tests/mypy_test.py"
+    - python: "2.7"
+      env: TEST_CMD="./tests/pytype_test.py --num-parallel=4"
 
 install:
-  - pip install -U git+git://github.com/python/mypy
+  # pytype needs py-2.7, mypy needs py-3.2+. Additional logic in runtests.py
+  - if [[ $TRAVIS_PYTHON_VERSION == '3.5' ]]; then pip install -U git+git://github.com/python/mypy; fi
+  - if [[ $TRAVIS_PYTHON_VERSION == '2.7' ]]; then pip install -U git+git://github.com/google/pytype; fi
 
 script:
-  - ./runtests.py -p3.5
-  - ./runtests.py -p3.4
-  - ./runtests.py -p3.3
-  - ./runtests.py -p3.2
-  - ./runtests.py -p2.7
+  - $TEST_CMD
+