doctor: add package for running in-depth healthchecks; use in bugreport (#5413)

Change-Id: Iaa4e5b021a545447f319cfe8b3da2bd3e5e5782b
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>

doctor/doctor_test.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2022 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 doctor
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"tailscale.com/types/logger"
+)
+
+func TestRunChecks(t *testing.T) {
+	c := qt.New(t)
+	var (
+		mu    sync.Mutex
+		lines []string
+	)
+	logf := func(format string, args ...any) {
+		mu.Lock()
+		defer mu.Unlock()
+		lines = append(lines, fmt.Sprintf(format, args...))
+	}
+
+	ctx := context.Background()
+	RunChecks(ctx, logf,
+		testCheck1{},
+		CheckFunc("testcheck2", func(_ context.Context, log logger.Logf) error {
+			log("check 2")
+			return nil
+		}),
+	)
+
+	mu.Lock()
+	defer mu.Unlock()
+	c.Assert(lines, qt.Contains, "testcheck1: check 1")
+	c.Assert(lines, qt.Contains, "testcheck2: check 2")
+}
+
+type testCheck1 struct{}
+
+func (t testCheck1) Name() string { return "testcheck1" }
+func (t testCheck1) Run(_ context.Context, log logger.Logf) error {
+	log("check 1")
+	return nil
+}