fix some print format errors

metadata/metadata_test.go

diff --git a/metadata/metadata_test.go b/metadata/metadata_test.go
index b2082d0..02e6ba5 100644
--- a/metadata/metadata_test.go
+++ b/metadata/metadata_test.go
@@ -101,7 +101,7 @@
 			t.Fatalf("Pairs(%v) = %v, want %v", test.kv, md, test.md)
 		}
 		if md.Len() != test.size {
-			t.Fatalf("Pairs(%v) generates md of size %d, want %d", md.Len(), test.size)
+			t.Fatalf("Pairs(%v) generates md of size %d, want %d", test.kv, md.Len(), test.size)
 		}
 	}
 }

picker.go

diff --git a/picker.go b/picker.go
index b83c859..50f315b 100644
--- a/picker.go
+++ b/picker.go
@@ -172,7 +172,7 @@
 			}
 			p.mu.Unlock()
 		default:
-			grpclog.Println("Unknown update.Op %d", update.Op)
+			grpclog.Println("Unknown update.Op ", update.Op)
 		}
 	}
 	return nil

test/end2end_test.go

diff --git a/test/end2end_test.go b/test/end2end_test.go
index be7691d..71d0204 100644
--- a/test/end2end_test.go
+++ b/test/end2end_test.go
@@ -537,7 +537,7 @@
 	}
 	ctx, _ = context.WithTimeout(context.Background(), time.Second)
 	if _, err := cc.WaitForStateChange(ctx, grpc.Ready); err == nil {
-		t.Fatalf("cc.WaitForStateChange(_, %s) = _, %v, want _, %v", grpc.Ready, context.DeadlineExceeded)
+		t.Fatalf("cc.WaitForStateChange(_, %s) = _, <nil>, want _, %v", grpc.Ready, context.DeadlineExceeded)
 	}
 	tc := testpb.NewTestServiceClient(cc)
 	var header metadata.MD