core, consensus: pluggable consensus engines (#3817)

This commit adds pluggable consensus engines to go-ethereum. In short, it
introduces a generic consensus interface, and refactors the entire codebase to
use this interface.

consensus/ethash/ethash_test.go

@@ -0,0 +1,40 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethash
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+// Tests that ethash works correctly in test mode.
+func TestTestMode(t *testing.T) {
+	head := &types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(100)}
+
+	ethash := NewTester()
+	block, err := ethash.Seal(nil, types.NewBlockWithHeader(head), nil)
+	if err != nil {
+		t.Fatalf("failed to seal block: %v", err)
+	}
+	head.Nonce = types.EncodeNonce(block.Nonce())
+	head.MixDigest = block.MixDigest()
+	if err := ethash.VerifySeal(nil, head); err != nil {
+		t.Fatalf("unexpected verification error: %v", err)
+	}
+}