core: restore tests

core/blockchain_test.go

@@ -1951,6 +1951,69 @@ func testInsertReceiptChainRollback(t *testing.T, scheme string) {
 	}
 }
 
+// Tests that importing a very large side fork, which is larger than the canon chain,
+// but where the difficulty per block is kept low: this means that it will not
+// overtake the 'canon' chain until after it's passed canon by about 200 blocks.
+//
+// Details at:
+//   - https://github.com/ethereum/go-ethereum/issues/18977
+//   - https://github.com/ethereum/go-ethereum/pull/18988
+func TestLowDiffLongChain(t *testing.T) {
+	testLowDiffLongChain(t, rawdb.HashScheme)
+	testLowDiffLongChain(t, rawdb.PathScheme)
+}
+
+func testLowDiffLongChain(t *testing.T, scheme string) {
+	// Generate a canonical chain to act as the main dataset
+	engine := ethash.NewFaker()
+	genesis := &Genesis{
+		Config:  params.TestChainConfig,
+		BaseFee: big.NewInt(params.InitialBaseFee),
+	}
+	// We must use a pretty long chain to ensure that the fork doesn't overtake us
+	// until after at least 128 blocks post tip
+	genDb, blocks, _ := GenerateChainWithGenesis(genesis, engine, 6*state.TriesInMemory, func(i int, b *BlockGen) {
+		b.SetCoinbase(common.Address{1})
+		b.OffsetTime(-9)
+	})
+
+	// Import the canonical chain
+	diskdb, _ := rawdb.NewDatabaseWithFreezer(rawdb.NewMemoryDatabase(), "", "", false)
+	defer diskdb.Close()
+
+	chain, err := NewBlockChain(diskdb, DefaultCacheConfigWithScheme(scheme), genesis, nil, engine, vm.Config{}, nil, nil)
+	if err != nil {
+		t.Fatalf("failed to create tester chain: %v", err)
+	}
+	defer chain.Stop()
+
+	if n, err := chain.InsertChain(blocks); err != nil {
+		t.Fatalf("block %d: failed to insert into chain: %v", n, err)
+	}
+	// Generate fork chain, starting from an early block
+	parent := blocks[10]
+	fork, _ := GenerateChain(genesis.Config, parent, engine, genDb, 8*state.TriesInMemory, func(i int, b *BlockGen) {
+		b.SetCoinbase(common.Address{2})
+	})
+
+	// And now import the fork
+	if i, err := chain.InsertChain(fork); err != nil {
+		t.Fatalf("block %d: failed to insert into chain: %v", i, err)
+	}
+	head := chain.CurrentBlock()
+	if got := fork[len(fork)-1].Hash(); got != head.Hash() {
+		t.Fatalf("head wrong, expected %x got %x", head.Hash(), got)
+	}
+	// Sanity check that all the canonical numbers are present
+	header := chain.CurrentHeader()
+	for number := head.Number.Uint64(); number > 0; number-- {
+		if hash := chain.GetHeaderByNumber(number).Hash(); hash != header.Hash() {
+			t.Fatalf("header %d: canonical hash mismatch: have %x, want %x", number, hash, header.Hash())
+		}
+		header = chain.GetHeader(header.ParentHash, number-1)
+	}
+}
+
 // Tests that importing a sidechain (S), where
 // - S is sidechain, containing blocks [Sn...Sm]
 // - C is canon chain, containing blocks [G..Cn..Cm]