Add all BENNC message types with unit tests

tests/messages/unsubscribe.test.ts

@@ -0,0 +1,14 @@
+import { MessageTypes } from '../../src/common'
+import { packers } from '../../src/mapping'
+
+test('Create an unsubscribe (0xffff) packet.', () => {
+  // Given
+  const messageType = 0xabcd
+
+  // When
+  const packedPacket = packers[MessageTypes.Unsubscribe]({ messageType: messageType })
+
+  // Then
+  const expectedResult = Buffer.from([0xff, 0xff, 0x00, 0x02, 0xab, 0xcd])
+  expect(packedPacket).toMatchObject(expectedResult)
+})