tstest: rename from testy.

Signed-off-by: David Anderson <danderson@tailscale.com>

tstest/log.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tstest
+
+import (
+	"log"
+	"os"
+	"testing"
+)
+
+type testLogWriter struct {
+	t *testing.T
+}
+
+func (w *testLogWriter) Write(b []byte) (int, error) {
+	w.t.Helper()
+	w.t.Logf("%s", b)
+	return len(b), nil
+}
+
+func FixLogs(t *testing.T) {
+	log.SetFlags(log.Ltime | log.Lshortfile)
+	log.SetOutput(&testLogWriter{t})
+}
+
+func UnfixLogs(t *testing.T) {
+	defer log.SetOutput(os.Stderr)
+}