Add unit tests for socket

lib/src/socket.dart

@@ -220,6 +220,7 @@ class PhoenixSocket {
       }
     } catch (err, stackTrace) {
       _logger.severe('Raised Exception', err, stackTrace);
+      print('||| CONNECT EXCEPTION: $err');
 
       _ws = null;
       _socketState = SocketState.closed;

test/socket_test.dart

@@ -0,0 +1,53 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:mockito/mockito.dart';
+import 'package:phoenix_socket/phoenix_socket.dart';
+import 'package:rxdart/rxdart.dart';
+import 'package:test/test.dart';
+
+import 'mocks.dart';
+
+void main() {
+  test('socket connect retries on unexpected error', () async {
+    final sink = MockWebSocketSink();
+    final websocket = MockWebSocketChannel();
+    final phoenixSocket = PhoenixSocket(
+      'endpoint',
+      webSocketChannelFactory: (_) => websocket,
+    );
+    int invocations = 0;
+    final excpetions = ['E', PhoenixException()];
+
+    when(websocket.sink).thenReturn(sink);
+
+    when(websocket.stream).thenAnswer((_) {
+      if (invocations < 2) {
+        // Return a never stream to keep the socket open on the first two
+        // attempts. If it is an empty Stream the socket will close immediately.
+        return NeverStream();
+      } else {
+        // Return a proper message on the third attempt which allows the socket
+        // to connect.
+        final controller = StreamController<String>()
+          ..add(jsonEncode(Message.heartbeat('$invocations').encode()));
+        return controller.stream;
+      }
+    });
+
+    // Throw an error adding data to the sink on the first two attempts.
+    // On the third attempt, the sink add should work as expected.
+    when(sink.add(any)).thenAnswer((_) {
+      if (invocations < 2) {
+        throw excpetions[invocations++];
+      }
+    });
+
+    // Connect to the socket
+    await phoenixSocket.connect();
+    expect(phoenixSocket.isConnected, isTrue);
+
+    // Expect the first two unexpected failures to be retried
+    verify(sink.add(any)).called(3);
+  });
+}