Support fig.y(a)ml and show a deprecation warning

Closes #864

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

tests/unit/cli_test.py

@@ -2,12 +2,15 @@ from __future__ import unicode_literals
 from __future__ import absolute_import
 import logging
 import os
+import tempfile
+import shutil
 from .. import unittest
 
 import mock
 
 from compose.cli import main
 from compose.cli.main import TopLevelCommand
+from compose.cli.errors import ComposeFileNotFound
 from six import StringIO
 
 
@@ -57,12 +60,30 @@ class CLITestCase(unittest.TestCase):
             project_name = command.get_project_name(None)
         self.assertEquals(project_name, name)
 
-    def test_yaml_filename_check(self):
-        command = TopLevelCommand()
-        command.base_dir = 'tests/fixtures/longer-filename-composefile'
-        with mock.patch('compose.cli.command.log', autospec=True) as mock_log:
-            self.assertTrue(command.get_config_path())
-        self.assertEqual(mock_log.warning.call_count, 2)
+    def test_filename_check(self):
+        self.assertEqual('docker-compose.yml', get_config_filename_for_files([
+            'docker-compose.yml',
+            'docker-compose.yaml',
+            'fig.yml',
+            'fig.yaml',
+        ]))
+
+        self.assertEqual('docker-compose.yaml', get_config_filename_for_files([
+            'docker-compose.yaml',
+            'fig.yml',
+            'fig.yaml',
+        ]))
+
+        self.assertEqual('fig.yml', get_config_filename_for_files([
+            'fig.yml',
+            'fig.yaml',
+        ]))
+
+        self.assertEqual('fig.yaml', get_config_filename_for_files([
+            'fig.yaml',
+        ]))
+
+        self.assertRaises(ComposeFileNotFound, lambda: get_config_filename_for_files([]))
 
     def test_get_project(self):
         command = TopLevelCommand()
@@ -81,3 +102,21 @@ class CLITestCase(unittest.TestCase):
         main.setup_logging()
         self.assertEqual(logging.getLogger().level, logging.DEBUG)
         self.assertEqual(logging.getLogger('requests').propagate, False)
+
+
+def get_config_filename_for_files(filenames):
+    project_dir = tempfile.mkdtemp()
+    try:
+        make_files(project_dir, filenames)
+        command = TopLevelCommand()
+        command.base_dir = project_dir
+        return os.path.basename(command.get_config_path())
+    finally:
+        shutil.rmtree(project_dir)
+
+
+def make_files(dirname, filenames):
+    for fname in filenames:
+        with open(os.path.join(dirname, fname), 'w') as f:
+            f.write('')
+