Support multiple files in COMPOSE_FILE env var.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

tests/unit/cli/command_test.py

@@ -1,16 +1,19 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 
+import os
+
 import pytest
 from requests.exceptions import ConnectionError
 
 from compose.cli import errors
 from compose.cli.command import friendly_error_message
+from compose.cli.command import get_config_path_from_options
+from compose.const import IS_WINDOWS_PLATFORM
 from tests import mock
-from tests import unittest
 
 
-class FriendlyErrorMessageTestCase(unittest.TestCase):
+class TestFriendlyErrorMessage(object):
 
     def test_dispatch_generic_connection_error(self):
         with pytest.raises(errors.ConnectionErrorGeneric):
@@ -21,3 +24,31 @@ class FriendlyErrorMessageTestCase(unittest.TestCase):
             ):
                 with friendly_error_message():
                     raise ConnectionError()
+
+
+class TestGetConfigPathFromOptions(object):
+
+    def test_path_from_options(self):
+        paths = ['one.yml', 'two.yml']
+        opts = {'--file': paths}
+        assert get_config_path_from_options(opts) == paths
+
+    def test_single_path_from_env(self):
+        with mock.patch.dict(os.environ):
+            os.environ['COMPOSE_FILE'] = 'one.yml'
+            assert get_config_path_from_options({}) == ['one.yml']
+
+    @pytest.mark.skipif(IS_WINDOWS_PLATFORM, reason='posix separator')
+    def test_multiple_path_from_env(self):
+        with mock.patch.dict(os.environ):
+            os.environ['COMPOSE_FILE'] = 'one.yml:two.yml'
+            assert get_config_path_from_options({}) == ['one.yml', 'two.yml']
+
+    @pytest.mark.skipif(not IS_WINDOWS_PLATFORM, reason='windows separator')
+    def test_multiple_path_from_env_windows(self):
+        with mock.patch.dict(os.environ):
+            os.environ['COMPOSE_FILE'] = 'one.yml;two.yml'
+            assert get_config_path_from_options({}) == ['one.yml', 'two.yml']
+
+    def test_no_path(self):
+        assert not get_config_path_from_options({})