Refactored the startup reply in the fake PostgreSQL server in the Persistence tests target.

Packages/Persistence/Tests/Utils/Fakes/PlaintextPostgresServer.swift

@@ -99,7 +99,7 @@ private extension PlaintextPostgresServer {
             context: ChannelHandlerContext,
             data: NIOAny
         ) {
-            var buffer = unwrapInboundIn(data)
+            let buffer = unwrapInboundIn(data)
 
             switch state {
             case .awaitingSSLRequest:
@@ -107,13 +107,7 @@ private extension PlaintextPostgresServer {
                 // 'N', while a direct startup message (a client connecting with TLS disabled) is
                 // answered straight away.
                 guard buffer.getInteger(at: buffer.readerIndex + 4, as: Int32.self) == Self.sslRequestCode else {
-                    state = .established
+                    completeStartup(context: context)
-
-                    context.writeAndFlush(
-                        wrapOutboundOut(Self.startupResponse(allocator: context.channel.allocator)),
-                        promise: nil
-                    )
-
                     return
                 }
 
@@ -128,17 +122,22 @@ private extension PlaintextPostgresServer {
                     promise: nil
                 )
             case .awaitingStartup:
-                state = .established
+                completeStartup(context: context)
-
-                context.writeAndFlush(
-                    wrapOutboundOut(Self.startupResponse(allocator: context.channel.allocator)),
-                    promise: nil
-                )
             case .established:
                 context.close(promise: nil)
             }
         }
 
+        /// Answers a startup message and marks the connection established.
+        private func completeStartup(context: ChannelHandlerContext) {
+            state = .established
+
+            context.writeAndFlush(
+                wrapOutboundOut(Self.startupResponse(allocator: context.channel.allocator)),
+                promise: nil
+            )
+        }
+
         // MARK: Helpers
 
         /// The reply completing a plaintext startup: `AuthenticationOk`, `BackendKeyData`, and