Support passing an alternate environment dict to kwargs_from_env

Signed-off-by: Joffrey F <joffrey@docker.com>

docker/utils/utils.py

@@ -479,15 +479,17 @@ def parse_devices(devices):
     return device_list
 
 
-def kwargs_from_env(ssl_version=None, assert_hostname=None):
-    host = os.environ.get('DOCKER_HOST')
+def kwargs_from_env(ssl_version=None, assert_hostname=None, environment=None):
+    if not environment:
+        environment = os.environ
+    host = environment.get('DOCKER_HOST')
 
     # empty string for cert path is the same as unset.
-    cert_path = os.environ.get('DOCKER_CERT_PATH') or None
+    cert_path = environment.get('DOCKER_CERT_PATH') or None
 
     # empty string for tls verify counts as "false".
     # Any value or 'unset' counts as true.
-    tls_verify = os.environ.get('DOCKER_TLS_VERIFY')
+    tls_verify = environment.get('DOCKER_TLS_VERIFY')
     if tls_verify == '':
         tls_verify = False
     else:

tests/unit/utils_test.py

@@ -249,6 +249,20 @@ class KwargsFromEnvTest(base.BaseTestCase):
             if temp_dir:
                 shutil.rmtree(temp_dir)
 
+    def test_kwargs_from_env_alternate_env(self):
+        # Values in os.environ are entirely ignored if an alternate is
+        # provided
+        os.environ.update(
+            DOCKER_HOST='tcp://192.168.59.103:2376',
+            DOCKER_CERT_PATH=TEST_CERT_DIR,
+            DOCKER_TLS_VERIFY=''
+        )
+        kwargs = kwargs_from_env(environment={
+            'DOCKER_HOST': 'http://docker.gensokyo.jp:2581',
+        })
+        assert 'http://docker.gensokyo.jp:2581' == kwargs['base_url']
+        assert 'tls' not in kwargs
+
 
 class ConverVolumeBindsTest(base.BaseTestCase):
     def test_convert_volume_binds_empty(self):