feat: add base implementation for realtime communication

Signed-off-by: Philip Molares <philip.molares@udo.edu>
Signed-off-by: Erik Michelson <github@erik.michelson.eu>
Co-authored-by: Erik Michelson <github@erik.michelson.eu>
Co-authored-by: Philip Molares <philip.molares@udo.edu>
Co-authored-by: Tilman Vatteroth <git@tilmanvatteroth.de>
Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

src/realtime/realtime-note/test-utils/mock-realtime-note.ts

@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { EventEmitter } from 'events';
+import { Mock } from 'ts-mockery';
+import TypedEmitter from 'typed-emitter';
+
+import { RealtimeNote, RealtimeNoteEvents } from '../realtime-note';
+import { WebsocketAwareness } from '../websocket-awareness';
+import { WebsocketDoc } from '../websocket-doc';
+
+class MockRealtimeNote extends (EventEmitter as new () => TypedEmitter<RealtimeNoteEvents>) {
+  constructor(
+    private doc: WebsocketDoc,
+    private awareness: WebsocketAwareness,
+  ) {
+    super();
+  }
+
+  public getYDoc(): WebsocketDoc {
+    return this.doc;
+  }
+
+  public getAwareness(): WebsocketAwareness {
+    return this.awareness;
+  }
+
+  public removeClient(): void {
+    //left blank for mock
+  }
+}
+
+/**
+ * Provides a partial mock for {@link RealtimeNote}
+ * @param doc Defines the return value for `getYDoc`
+ * @param awareness Defines the return value for `getAwareness`
+ */
+export function mockRealtimeNote(
+  doc: WebsocketDoc,
+  awareness: WebsocketAwareness,
+): RealtimeNote {
+  return Mock.from<RealtimeNote>(new MockRealtimeNote(doc, awareness));
+}