Stop using print in certbot.main module. (#5121)

* Stop using print in `certbot.main` module.

* Update certbot.main.plugins_cmd` function.

* Update test methods `test_plugins_no_args`,
`test_plugins_no_args_unprivileged`, `test_plugins_init` and
`test_plugins_prepare` in `cerbot.tests.MainTest` class.

Addresses #3720.

* certbot: Add `patch_get_utility_with_stdout` function.

* Add functions `certbot.tests.util.patch_get_utility_with_stdout`
  and `certbot.tests.util._create_get_utility_mock_with_stdout`.

* certbot: tests: Update tests in MainTest.

* Update methods `test_plugins_no_args`,
`test_plugins_no_args_unprivileged`, and `test_plugins_init`,
`test_plugins_prepare` to use `patch_get_utility_with_stdout`.

* certbot: tests: Update _create_get_utility_mock_with_stdout.

* Update certbot.tests.util._create_get_utility_mock_with_stdout
  function. The mock function for all IDisplay methods, except
  `notification` method, calls _write_msg and _assert_valid_call.

* certbot: tests: Update `patch_get_utility_with_stdout`

* Update doc string.
* Argument stdout's default value is None now.

* certbot: tests: Update util._create_get_utility_mock_with_stdout.

certbot/main.py

@@ -1,5 +1,6 @@
 """Certbot main entry point."""
 from __future__ import print_function
+import functools
 import logging.handlers
 import os
 import sys
@@ -492,7 +493,7 @@ def install(config, plugins):
     _install_cert(config, le_client, domains)
 
 
-def plugins_cmd(config, plugins):  # TODO: Use IDisplay rather than print
+def plugins_cmd(config, plugins):
     """List server software plugins."""
     logger.debug("Expected interfaces: %s", config.ifaces)
 
@@ -500,8 +501,10 @@ def plugins_cmd(config, plugins):  # TODO: Use IDisplay rather than print
     filtered = plugins.visible().ifaces(ifaces)
     logger.debug("Filtered plugins: %r", filtered)
 
+    notify = functools.partial(zope.component.getUtility(
+        interfaces.IDisplay).notification, pause=False)
     if not config.init and not config.prepare:
-        print(str(filtered))
+        notify(str(filtered))
         return
 
     filtered.init(config)
@@ -509,13 +512,13 @@ def plugins_cmd(config, plugins):  # TODO: Use IDisplay rather than print
     logger.debug("Verified plugins: %r", verified)
 
     if not config.prepare:
-        print(str(verified))
+        notify(str(verified))
         return
 
     verified.prepare()
     available = verified.available()
     logger.debug("Prepared plugins: %s", available)
-    print(str(available))
+    notify(str(available))
 
 
 def rollback(config, plugins):

certbot/tests/main_test.py

@@ -539,7 +539,10 @@ class MainTest(test_util.ConfigTestCase):  # pylint: disable=too-many-public-met
         ifaces = []
         plugins = mock_disco.PluginsRegistry.find_all()
 
-        _, stdout, _, _ = self._call(['plugins'])
+        stdout = six.StringIO()
+        with test_util.patch_get_utility_with_stdout(stdout=stdout):
+            _, stdout, _, _ = self._call(['plugins'], stdout)
+
         plugins.visible.assert_called_once_with()
         plugins.visible().ifaces.assert_called_once_with(ifaces)
         filtered = plugins.visible().ifaces()
@@ -556,14 +559,16 @@ class MainTest(test_util.ConfigTestCase):  # pylint: disable=too-many-public-met
             _, _, _, _ = directory, mode, uid, strict
             raise errors.Error()
 
+        stdout = six.StringIO()
         with mock.patch('certbot.util.set_up_core_dir') as mock_set_up_core_dir:
-            mock_set_up_core_dir.side_effect = throw_error
+            with test_util.patch_get_utility_with_stdout(stdout=stdout):
+                mock_set_up_core_dir.side_effect = throw_error
+                _, stdout, _, _ = self._call(['plugins'], stdout)
 
-            _, stdout, _, _ = self._call(['plugins'])
-            plugins.visible.assert_called_once_with()
-            plugins.visible().ifaces.assert_called_once_with(ifaces)
-            filtered = plugins.visible().ifaces()
-            self.assertEqual(stdout.getvalue().strip(), str(filtered))
+        plugins.visible.assert_called_once_with()
+        plugins.visible().ifaces.assert_called_once_with(ifaces)
+        filtered = plugins.visible().ifaces()
+        self.assertEqual(stdout.getvalue().strip(), str(filtered))
 
     @mock.patch('certbot.main.plugins_disco')
     @mock.patch('certbot.main.cli.HelpfulArgumentParser.determine_help_topics')
@@ -571,7 +576,10 @@ class MainTest(test_util.ConfigTestCase):  # pylint: disable=too-many-public-met
         ifaces = []
         plugins = mock_disco.PluginsRegistry.find_all()
 
-        _, stdout, _, _ = self._call(['plugins', '--init'])
+        stdout = six.StringIO()
+        with test_util.patch_get_utility_with_stdout(stdout=stdout):
+            _, stdout, _, _ = self._call(['plugins', '--init'], stdout)
+
         plugins.visible.assert_called_once_with()
         plugins.visible().ifaces.assert_called_once_with(ifaces)
         filtered = plugins.visible().ifaces()
@@ -585,7 +593,11 @@ class MainTest(test_util.ConfigTestCase):  # pylint: disable=too-many-public-met
     def test_plugins_prepare(self, _det, mock_disco):
         ifaces = []
         plugins = mock_disco.PluginsRegistry.find_all()
-        _, stdout, _, _ = self._call(['plugins', '--init', '--prepare'])
+
+        stdout = six.StringIO()
+        with test_util.patch_get_utility_with_stdout(stdout=stdout):
+            _, stdout, _, _ = self._call(['plugins', '--init', '--prepare'], stdout)
+
         plugins.visible.assert_called_once_with()
         plugins.visible().ifaces.assert_called_once_with(ifaces)
         filtered = plugins.visible().ifaces()

certbot/tests/util.py

@@ -14,6 +14,7 @@ from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import serialization
 import mock
 import OpenSSL
+import six
 from six.moves import reload_module  # pylint: disable=import-error
 
 from acme import jose
@@ -169,6 +170,30 @@ def patch_get_utility(target='zope.component.getUtility'):
     return mock.patch(target, new_callable=_create_get_utility_mock)
 
 
+def patch_get_utility_with_stdout(target='zope.component.getUtility',
+                                  stdout=None):
+    """Patch zope.component.getUtility to use a special mock IDisplay.
+
+    The mock IDisplay works like a regular mock object, except it also
+    also asserts that methods are called with valid arguments.
+
+    The `message` argument passed to the IDisplay methods is passed to
+    stdout's write method.
+
+    :param str target: path to patch
+    :param object stdout: object to write standard output to; it is
+        expected to have a `write` method
+
+    :returns: mock zope.component.getUtility
+    :rtype: mock.MagicMock
+
+    """
+    stdout = stdout if stdout else six.StringIO()
+
+    freezable_mock = _create_get_utility_mock_with_stdout(stdout)
+    return mock.patch(target, new=freezable_mock)
+
+
 class FreezableMock(object):
     """Mock object with the ability to freeze attributes.
 
@@ -249,6 +274,36 @@ def _create_get_utility_mock():
     return FreezableMock(frozen=True, return_value=display)
 
 
+def _create_get_utility_mock_with_stdout(stdout):
+    def _write_msg(message, *unused_args, **unused_kwargs):
+        """Write to message to stdout.
+        """
+        if message:
+            stdout.write(message)
+
+    def mock_method(*args, **kwargs):
+        """
+        Mock function for IDisplay methods.
+        """
+        _assert_valid_call(args, kwargs)
+        _write_msg(*args, **kwargs)
+
+
+    display = FreezableMock()
+    for name in interfaces.IDisplay.names():  # pylint: disable=no-member
+        if name == 'notification':
+            frozen_mock = FreezableMock(frozen=True,
+                                        func=_write_msg)
+            setattr(display, name, frozen_mock)
+        else:
+            frozen_mock = FreezableMock(frozen=True,
+                                        func=mock_method)
+            setattr(display, name, frozen_mock)
+    display.freeze()
+
+    return FreezableMock(frozen=True, return_value=display)
+
+
 def _assert_valid_call(*args, **kwargs):
     assert_args = [args[0] if args else kwargs['message']]