ssh/test: fix test goroutine error handling

Adds an error channel to the test helper function
testPortForward() to collect errors that happen inside
a goroutine.

Change-Id: I6db1d24b935fdfad637c971581ae80beaebd8a1f
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/207462
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ssh/test/forward_unix_test.go

@@ -8,6 +8,7 @@ package test
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -31,17 +32,21 @@ func testPortForward(t *testing.T, n, listenAddr string) {
 		t.Fatal(err)
 	}
 
+	errCh := make(chan error, 1)
+
 	go func() {
+		defer close(errCh)
 		sshConn, err := sshListener.Accept()
 		if err != nil {
-			t.Fatalf("listen.Accept failed: %v", err)
+			errCh <- fmt.Errorf("listen.Accept failed: %v", err)
+			return
 		}
+		defer sshConn.Close()
 
 		_, err = io.Copy(sshConn, sshConn)
 		if err != nil && err != io.EOF {
-			t.Fatalf("ssh client copy: %v", err)
+			errCh <- fmt.Errorf("ssh client copy: %v", err)
 		}
-		sshConn.Close()
 	}()
 
 	forwardedAddr := sshListener.Addr().String()
@@ -76,6 +81,12 @@ func testPortForward(t *testing.T, n, listenAddr string) {
 		t.Errorf("netConn.CloseWrite: %v", err)
 	}
 
+	// Check for errors on server goroutine
+	err = <-errCh
+	if err != nil {
+		t.Fatalf("server: %v", err)
+	}
+
 	read := <-readChan
 
 	if len(sent) != len(read) {