eth/downloader: fix downloadTesterPeer to use fake TD

.*Starvation.* tests were failing because
errStallingPeer was expected but no error received.
The TD is advertised and assigned to the downloader
as expected, but the handshake with the peer's Head
method was causing the reassignment of the downloader.td
field to the actual (honest) TD value by virtue of
the virtuous dlp.Head method, which returned the actual
chain TD.
This caused the tests to fail because the sync TD was
not the fake one.
So this patch provides a field in the tester peer type
to actually handle lying about TD, which then
make the errStallingPeer error get returned.

Date: 2023-05-17 07:27:56-07:00
Signed-off-by: meows <b5c6@protonmail.com>

eth/downloader/downloader_test.go

@@ -154,13 +154,18 @@ type downloadTesterPeer struct {
 	chain *core.BlockChain
 
 	withholdHeaders map[common.Hash]struct{}
+	fakeTD          *big.Int
 }
 
 // Head constructs a function to retrieve a peer's current head hash
 // and total difficulty.
 func (dlp *downloadTesterPeer) Head() (common.Hash, *big.Int, *big.Int) {
 	head := dlp.chain.CurrentBlock()
-	return head.Hash(), dlp.chain.GetTd(head.Hash(), head.Number.Uint64()), new(big.Int).Set(dlp.chain.CurrentBlock().Difficulty)
+	td := dlp.chain.GetTd(head.Hash(), head.Number.Uint64())
+	if dlp.fakeTD != nil {
+		td.Set(dlp.fakeTD)
+	}
+	return head.Hash(), td, new(big.Int).Set(dlp.chain.CurrentBlock().Difficulty)
 }
 
 // SetHead constructs a function to retrieve a peer's current head hash
@@ -992,8 +997,10 @@ func testHighTDStarvationAttack(t *testing.T, protocol uint, mode SyncMode) {
 	defer tester.terminate()
 
 	chain := testChainBase.shorten(1)
-	tester.newPeer("attack", protocol, chain.blocks[1:])
-	if err := tester.sync("attack", big.NewInt(1000000), mode); err != errStallingPeer {
+	dlp := tester.newPeer("attack", protocol, chain.blocks[1:])
+	fakeTD := big.NewInt(1000000)
+	dlp.fakeTD = fakeTD
+	if err := tester.sync("attack", fakeTD, mode); err != errStallingPeer {
 		t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errStallingPeer)
 	}
 }