Fix that api_workers=0 doesn't spawn any api workers

Change-Id: Iadb9b35bc189244dee293efe042fee77a9a2d7da
Closes-Bug: 1607691
(cherry picked from commit ffeae31505)

neutron/service.py

@@ -225,7 +225,7 @@ def serve_rpc():
 
 def _get_api_workers():
     workers = cfg.CONF.api_workers
-    if not workers:
+    if workers is None:
         workers = processutils.get_worker_count()
     return workers
 

neutron/tests/unit/test_service.py

@@ -15,7 +15,10 @@
 
 import mock
 
+from oslo_config import cfg
+
 from neutron import service
+from neutron.tests import base
 from neutron.tests.unit import test_wsgi
 
 
@@ -25,3 +28,30 @@ class TestRpcWorker(test_wsgi.TestServiceBase):
         _plugin = mock.Mock()
         rpc_worker = service.RpcWorker(_plugin)
         self._test_reset(rpc_worker)
+
+
+class TestRunWsgiApp(base.BaseTestCase):
+    def setUp(self):
+        super(TestRunWsgiApp, self).setUp()
+        self.processor_count = mock.patch(
+            'oslo_concurrency.processutils.get_worker_count'
+        ).start().return_value
+
+    def _test_api_workers(self, config_value, expected_passed_value):
+        if config_value is not None:
+            cfg.CONF.set_override('api_workers', config_value)
+        with mock.patch('neutron.wsgi.Server') as mock_server:
+            service.run_wsgi_app(mock.sentinel.app)
+        start_call = mock_server.return_value.start.call_args
+        expected_call = mock.call(
+            mock.ANY, mock.ANY, mock.ANY, workers=expected_passed_value)
+        self.assertEqual(expected_call, start_call)
+
+    def test_api_workers_zero(self):
+        self._test_api_workers(0, 0)
+
+    def test_api_workers_default(self):
+        self._test_api_workers(None, self.processor_count)
+
+    def test_api_workers_defined(self):
+        self._test_api_workers(42, 42)