ipn: mock controlclient.Client; big ipn.Backend state machine test.

A very long unit test that verifies the way the controlclient and
ipn.Backend interact.

This is a giant sequential test of the state machine. The test passes,
but only because it's asserting all the wrong behaviour. I marked all
the behaviour I think is wrong with BUG comments, and several
additional test opportunities with TODO.

Note: the new test supercedes TestStartsInNeedsLoginState, which was
checking for incorrect behaviour (although the new test still checks
for the same incorrect behaviour) and assumed .Start() would converge
before returning, which it happens to do, but only for this very
specific case, for the current implementation. You're supposed to wait
for the notifications.

Updates: tailscale/corp#1660

Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>

ipn/ipnlocal/local_test.go

@@ -5,11 +5,9 @@
 package ipnlocal
 
 import (
-	"bytes"
 	"fmt"
 	"net/http"
 	"reflect"
-	"sync"
 	"testing"
 	"time"
 
@@ -434,45 +432,6 @@ func (panicOnUseTransport) RoundTrip(*http.Request) (*http.Response, error) {
 	panic("unexpected HTTP request")
 }
 
-var nl = []byte("\n")
-
-func TestStartsInNeedsLoginState(t *testing.T) {
-	var (
-		mu     sync.Mutex
-		logBuf bytes.Buffer
-	)
-	logf := func(format string, a ...interface{}) {
-		mu.Lock()
-		defer mu.Unlock()
-		fmt.Fprintf(&logBuf, format, a...)
-		if !bytes.HasSuffix(logBuf.Bytes(), nl) {
-			logBuf.Write(nl)
-		}
-	}
-	store := new(ipn.MemoryStore)
-	eng, err := wgengine.NewFakeUserspaceEngine(logf, 0)
-	if err != nil {
-		t.Fatalf("NewFakeUserspaceEngine: %v", err)
-	}
-	lb, err := NewLocalBackend(logf, "logid", store, eng)
-	if err != nil {
-		t.Fatalf("NewLocalBackend: %v", err)
-	}
-
-	lb.SetHTTPTestClient(&http.Client{
-		Transport: panicOnUseTransport{}, // validate we don't send HTTP requests
-	})
-
-	if err := lb.Start(ipn.Options{
-		StateKey: ipn.GlobalDaemonStateKey,
-	}); err != nil {
-		t.Fatalf("Start: %v", err)
-	}
-	if st := lb.State(); st != ipn.NeedsLogin {
-		t.Errorf("State = %v; want NeedsLogin", st)
-	}
-}
-
 // Issue 1573: don't generate a machine key if we don't want to be running.
 func TestLazyMachineKeyGeneration(t *testing.T) {
 	defer func(old bool) { panicOnMachineKeyGeneration = old }(panicOnMachineKeyGeneration)