Fix test: check container's Env array instead of the output of 'env'

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

tests/acceptance/cli_test.py

@@ -1220,9 +1220,13 @@ def test_run_handles_sigterm(self):
     def test_run_env_values_from_system(self):
         os.environ['FOO'] = 'bar'
         os.environ['BAR'] = 'baz'
-        result = self.dispatch(['run', '-e', 'FOO', 'simple', 'env'], None)
-        assert 'FOO=bar' in result.stdout
-        assert 'BAR=baz' not in result.stdout
+
+        self.dispatch(['run', '-e', 'FOO', 'simple', 'true'], None)
+
+        container = self.project.containers(one_off=OneOffFilter.only, stopped=True)[0]
+        environment = container.get('Config.Env')
+        assert 'FOO=bar' in environment
+        assert 'BAR=baz' not in environment
 
     def test_rm(self):
         service = self.project.get_service('simple')