Add client/server version negotiation tests without mocks

* In src/client/index.test.ts added tests:
  - "should connect new client to old, supported server version"
  - should negotiate version when client is old, and newer server supports its version"
  - "should throw when client is old, and server doesn't support its version"

Author: cliffhall

src/client/index.test.ts

@@ -222,8 +222,6 @@ test("should connect new client to old, supported server version", async () => {
     server.connect(serverTransport),
   ]);
 
-  // These should work
-  // Connection should succeed with the older version
   expect(client.getServerVersion()).toEqual({
     name: "old server",
     version: "1.0",
@@ -287,8 +285,6 @@ test("should negotiate version when client is old, and newer server supports its
     server.connect(serverTransport),
   ]);
 
-  // These should work
-  // Connection should succeed with the older version
   expect(client.getServerVersion()).toEqual({
     name: "new server",
     version: "1.0",
@@ -348,9 +344,6 @@ test("should throw when client is old, and server doesn't support its version",
       },
   );
 
-  let closed = false;
-  clientTransport.onerror = () => {closed = true};
-
   await Promise.all([
     expect(client.connect(clientTransport)).rejects.toThrow(
         "Server's protocol version is not supported: FUTURE_VERSION"