tests: Add pytests for class FullMsgView.

With this ending commit:
 * A tested 'full message view' is added.
 * Fixes #543 (v1).
 * Allows user to view source message also by cycling the message
   content.

Author: Ezio-Sarthak

tests/ui_tools/test_popups.py

@@ -5,8 +5,9 @@
 
 from zulipterminal.config.keys import is_command_key, keys_for_command
 from zulipterminal.ui_tools.views import (
-    AboutView, EditHistoryView, EditModeView, HelpView, MsgInfoView,
-    PopUpConfirmationView, PopUpView, StreamInfoView, StreamMembersView,
+    AboutView, EditHistoryView, EditModeView, FullMsgView, HelpView,
+    MsgInfoView, PopUpConfirmationView, PopUpView, StreamInfoView,
+    StreamMembersView,
 )
 from zulipterminal.version import MINIMUM_SUPPORTED_SERVER_VERSION, ZT_VERSION
 
@@ -177,6 +178,107 @@ def test_feature_level_content(self, mocker, zulip_version):
         )
 
 
+class TestFullMsgView:
+    @pytest.fixture(autouse=True)
+    def mock_external_classes(self, mocker, msg_box):
+        self.content = msg_box.widget_list[2].original_widget[-1]
+        self.controller = mocker.Mock()
+        mocker.patch.object(self.controller, 'maximum_popup_dimensions',
+                            return_value=(64, 64))
+        self.controller.model.client.get_raw_message = (
+            mocker.Mock(return_value={
+                'result': 'success',
+                "raw_content": "**Don't** forget your towel!",
+            })
+        )
+        mocker.patch(VIEWS + '.urwid.SimpleFocusListWalker', return_value=[])
+        # NOTE: Given that the FullMsgView just uses the message ID from
+        # the message data currently, message_fixture is not used to avoid
+        # adding extra test runs unnecessarily.
+        self.message = {'id': 1}
+        self.full_msg_view = FullMsgView(
+            controller=self.controller,
+            message=self.message,
+            message_links=OrderedDict(),
+            time_mentions=list(),
+            content=self.content,
+            title='Full Message View',
+        )
+
+    def test_init(self, msg_box):
+        assert self.full_msg_view.controller == self.controller
+        assert self.full_msg_view.message == self.message
+        assert self.full_msg_view.message_links == OrderedDict()
+        assert self.full_msg_view.time_mentions == list()
+        assert self.full_msg_view.msg_body[0] == self.content
+        assert len(self.full_msg_view.msg_body[1].widget_list) == 2
+        assert self.full_msg_view.focus_tab == 0
+        self.controller.model.client.get_raw_message.assert_called_once_with(
+            self.message['id'],
+        )
+
+    @pytest.mark.parametrize('key', keys_for_command('MSG_INFO'))
+    def test_keypress_exit_popup(self, key, widget_size):
+        size = widget_size(self.full_msg_view)
+
+        self.full_msg_view.keypress(size, key)
+
+        assert self.controller.exit_popup.called
+
+    def test_keypress_exit_popup_invalid_key(self, widget_size):
+        size = widget_size(self.full_msg_view)
+        key = 'a'
+
+        self.full_msg_view.keypress(size, key)
+
+        assert not self.controller.exit_popup.called
+
+    @pytest.mark.parametrize('key', {*keys_for_command('FULL_MSG_VIEW'),
+                                     *keys_for_command('GO_BACK')})
+    def test_keypress_show_msg_info(self, key, widget_size):
+        size = widget_size(self.full_msg_view)
+
+        self.full_msg_view.keypress(size, key)
+
+        self.controller.show_msg_info.assert_called_once_with(
+            msg=self.message,
+            message_links=OrderedDict(),
+            time_mentions=list(),
+        )
+
+    def test_keypress_navigation(self, mocker, widget_size,
+                                 navigation_key_expected_key_pair):
+        size = widget_size(self.full_msg_view)
+        key, expected_key = navigation_key_expected_key_pair
+        super_keypress = mocker.patch(VIEWS + '.urwid.ListBox.keypress')
+
+        self.full_msg_view.keypress(size, key)
+
+        super_keypress.assert_called_once_with(size, expected_key)
+
+    @pytest.mark.parametrize('initial_foc_tab, expected_foc_tab', [
+            (0, 1),
+            (1, 0),
+        ],
+        ids=[
+            'rendered_msg_to_raw_msg',
+            'raw_msg_to_rendered_msg',
+        ]
+    )
+    @pytest.mark.parametrize("tab_key",
+                             keys_for_command("CYCLE_COMPOSE_FOCUS"))
+    def test_keypress_CYCLE_COMPOSE_FOCUS(self, mocker, initial_foc_tab,
+                                          expected_foc_tab, widget_size,
+                                          tab_key):
+
+        self.full_msg_view.focus_tab = initial_foc_tab
+        size = widget_size(self.full_msg_view)
+
+        self.full_msg_view.keypress(size, tab_key)
+
+        assert self.full_msg_view.focus_tab == expected_foc_tab
+
+
 class TestEditHistoryView:
     @pytest.fixture(autouse=True)
     def mock_external_classes(self, mocker):