Run tests on OS X

We import the scripts from ycmd with a couple of modifications:
 - don't set YCM_CORES=1 as we didn't before, and this makes the build a lot faster
 - don't install gcc-4.8 as we didn't before
 - install argparse as it is not available in python2.6

.travis.yml

@@ -1,9 +1,28 @@
-language: python
-python:
-  - "2.6"
-  - "2.7"
+language: generic
+os:
+  - linux
+  - osx
+sudo: false
 before_install:
   - git submodule update --init --recursive
 install:
-  - pip install -r python/test_requirements.txt
+  # source because it sets up env vars on some platforms
+  - source travis/travis_install.sh
 script: ./run_tests.py
+env:
+  matrix:
+    - YCMD_PYTHON_VERSION=2.7
+    - YCMD_PYTHON_VERSION=2.6
+addons:
+  apt:
+    sources:
+     - deadsnakes
+    packages:
+     - python2.6
+     - python2.6-dev
+     - python2.7
+     - python2.7-dev
+     - python-virtualenv
+cache:
+  directories:
+    - $HOME/.cache/pip

python/test_requirements.txt

@@ -2,4 +2,4 @@ flake8>=2.0
 mock>=1.0.1
 nose>=1.3.0
 PyHamcrest>=1.8.0
-
+argparse>=1.4.0

travis/travis_install.linux.sh

@@ -0,0 +1,3 @@
+# Linux installation
+
+virtualenv -p python${YCMD_PYTHON_VERSION} ${YCMD_VENV_DIR}

travis/travis_install.osx.sh

@@ -0,0 +1,19 @@
+# OS X installation
+
+# OS X comes with 2 versions of python by default, and a neat system
+# (versioner) to switch between them:
+#   /usr/bin/python2.7 - python 2.7
+#   /usr/bin/python2.6 - python 2.6
+#
+# We just set the system default to match it
+# http://stackoverflow.com/q/6998545
+defaults write com.apple.versioner.python Version ${YCMD_PYTHON_VERSION}
+
+# virtualenv is not installed by default on OS X under python2.6, and we don't
+# have sudo, so we install it manually. There is no "latest" link, so we have
+# to install a specific version.
+VENV_VERSION=13.1.2
+
+curl -O https://pypi.python.org/packages/source/v/virtualenv/virtualenv-${VENV_VERSION}.tar.gz
+tar xvfz virtualenv-${VENV_VERSION}.tar.gz
+python virtualenv-${VENV_VERSION}/virtualenv.py -p python${YCMD_PYTHON_VERSION} ${YCMD_VENV_DIR}

travis/travis_install.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+set -ev
+
+YCMD_VENV_DIR=${HOME}/venvs/ycmd_test
+
+# Requirements of OS-specific install:
+#  - install any software which is not installed by Travis configuration
+#  - create (but don't activate) a virtualenv for the python version
+#    ${YCMD_PYTHON_VERSION} in the directory ${YCMD_VENV_DIR}, e.g.
+#    virtualenv -p python${YCMD_PYTHON_VERSION} ${YCMD_VENV_DIR}
+source travis/travis_install.${TRAVIS_OS_NAME}.sh
+
+# virtualenv doesn't copy python-config https://github.com/pypa/virtualenv/issues/169
+# but our build system uses it
+cp /usr/bin/python${YCMD_PYTHON_VERSION}-config ${YCMD_VENV_DIR}/bin/python-config
+
+# virtualenv script is noisy, so don't print every command
+set +v
+source ${YCMD_VENV_DIR}/bin/activate
+set -v
+
+# It is quite easy to get the above series of steps wrong. Verify that the
+# version of python actually in the path and used is the version that was
+# requested, and fail the build if we broke the travis setup
+python_version=$(python -c 'import sys; print "{0}.{1}".format( sys.version_info[0], sys.version_info[1] )')
+echo "Checking python version (actual ${python_version} vs expected ${YCMD_PYTHON_VERSION})"
+test ${python_version} == ${YCMD_PYTHON_VERSION}
+
+pip install -U pip wheel setuptools
+pip install -r python/test_requirements.txt
+
+# The build infrastructure prints a lot of spam after this script runs, so make
+# sure to disable printing, and failing on non-zero exit code after this script
+# finishes
+set +ev