cmd/testwrapper: move from corp; mark magicsock test as flaky

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ibab5860f5797b3db151d3c27855333e43a9088a4

cmd/testwrapper/flakytest/flakytest.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2023 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 flakytest contains test helpers for marking a test as flaky. For
+// tests run using cmd/testwrapper, a failed flaky test will cause tests to be
+// re-run a few time until they succeed or exceed our iteration limit.
+package flakytest
+
+import (
+	"os"
+	"regexp"
+	"testing"
+)
+
+// InTestWrapper returns whether or not this binary is running under our test
+// wrapper.
+func InTestWrapper() bool {
+	return os.Getenv("TS_IN_TESTWRAPPER") != ""
+}
+
+var issueRegexp = regexp.MustCompile(`\Ahttps://github\.com/tailscale/[a-zA-Z0-9_.-]+/issues/\d+\z`)
+
+// Mark sets the current test as a flaky test, such that if it fails, it will
+// be retried a few times on failure. issue must be a GitHub issue that tracks
+// the status of the flaky test being marked, of the format:
+//
+//	https://github.com/tailscale/myRepo-H3re/issues/12345
+func Mark(t *testing.T, issue string) {
+	if !issueRegexp.MatchString(issue) {
+		t.Fatalf("bad issue format: %q", issue)
+	}
+
+	if !InTestWrapper() {
+		return
+	}
+
+	t.Cleanup(func() {
+		if t.Failed() {
+			t.Logf("flakytest: signaling test wrapper to retry test")
+
+			// Signal to test wrapper that we should restart.
+			os.Exit(123)
+		}
+	})
+}