Experimental implementation for webapp plugins (#7185)

* Start of experimental implementation for webapp plugins

* Updates to webapp plugin architecture

* Update pluggable test

* Remove debug code

webapp/tests/plugins/pluggable.test.jsx

@@ -0,0 +1,50 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+import React from 'react';
+import {mount} from 'enzyme';
+import {IntlProvider} from 'react-intl';
+
+import Pluggable from 'plugins/pluggable/pluggable.jsx';
+import ProfilePopover from 'components/profile_popover.jsx';
+
+class ProfilePopoverPlugin extends React.PureComponent {
+    render() {
+        return <span>{'ProfilePopoverPlugin'}</span>;
+    }
+}
+
+describe('plugins/Pluggable', () => {
+    test('should match snapshot with overridden component', () => {
+        const wrapper = mount(
+            <Pluggable
+                components={{ProfilePopover: ProfilePopoverPlugin}}
+                theme={{}}
+            >
+                <ProfilePopover
+                    user={{}}
+                    src='src'
+                />
+            </Pluggable>
+        );
+        expect(wrapper).toMatchSnapshot();
+    });
+
+    test('should match snapshot with no overridden component', () => {
+        window.mm_config = {};
+        const wrapper = mount(
+            <IntlProvider>
+                <Pluggable
+                    components={{}}
+                    theme={{}}
+                >
+                    <ProfilePopover
+                        user={{}}
+                        src='src'
+                    />
+                </Pluggable>
+            </IntlProvider>
+        );
+        expect(wrapper).toMatchSnapshot();
+    });
+});