ssh: print server exit reason in tests

This helps debugging protocol violations by the client

Change-Id: I8e5486b49515b719bbe3de44daa489fb7434875a
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/171680
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ssh/session_test.go

@@ -35,7 +35,7 @@ func dial(handler serverType, t *testing.T) *Client {
 		}
 		conf.AddHostKey(testSigners["rsa"])
 
-		_, chans, reqs, err := NewServerConn(c1, &conf)
+		conn, chans, reqs, err := NewServerConn(c1, &conf)
 		if err != nil {
 			t.Fatalf("Unable to handshake: %v", err)
 		}
@@ -56,6 +56,9 @@ func dial(handler serverType, t *testing.T) *Client {
 				handler(ch, inReqs, t)
 			}()
 		}
+		if err := conn.Wait(); err != io.EOF {
+			t.Logf("server exit reason: %v", err)
+		}
 	}()
 
 	config := &ClientConfig{
@@ -358,10 +361,9 @@ func TestServerWindow(t *testing.T) {
 	}
 	written, err := copyNRandomly("stdin", serverStdin, origBuf, windowTestBytes)
 	if err != nil {
-		t.Fatalf("failed to copy origBuf to serverStdin: %v", err)
+		t.Errorf("failed to copy origBuf to serverStdin: %v", err)
-	}
+	} else if written != windowTestBytes {
-	if written != windowTestBytes {
+		t.Errorf("Wrote only %d of %d bytes to server", written, windowTestBytes)
-		t.Fatalf("Wrote only %d of %d bytes to server", written, windowTestBytes)
 	}
 
 	echoedBytes := <-result