Added test case for Header.Hash() (#4052)

* Added static Header.Hash() test case

* Added reflect test for Header.Hash()

* Check for zero values in test struct

types/block_test.go

@@ -4,8 +4,10 @@ import (
 	// it is ok to use math/rand here: we do not need a cryptographically secure random
 	// number generator here and we can run the tests a bit faster
 	"crypto/rand"
+	"encoding/hex"
 	"math"
 	"os"
+	"reflect"
 	"testing"
 	"time"
 
@@ -13,6 +15,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/tendermint/tendermint/crypto"
+	"github.com/tendermint/tendermint/crypto/merkle"
 	"github.com/tendermint/tendermint/crypto/tmhash"
 	cmn "github.com/tendermint/tendermint/libs/common"
 	tmtime "github.com/tendermint/tendermint/types/time"
@@ -240,6 +243,73 @@ func TestCommitValidateBasic(t *testing.T) {
 	}
 }
 
+func TestHeaderHash(t *testing.T) {
+	testCases := []struct {
+		desc       string
+		header     *Header
+		expectHash cmn.HexBytes
+	}{
+		{"Generates expected hash", &Header{
+			Version:            version.Consensus{Block: 1, App: 2},
+			ChainID:            "chainId",
+			Height:             3,
+			Time:               time.Date(2019, 10, 13, 16, 14, 44, 0, time.UTC),
+			NumTxs:             4,
+			TotalTxs:           5,
+			LastBlockID:        makeBlockID(make([]byte, tmhash.Size), 6, make([]byte, tmhash.Size)),
+			LastCommitHash:     tmhash.Sum([]byte("last_commit_hash")),
+			DataHash:           tmhash.Sum([]byte("data_hash")),
+			ValidatorsHash:     tmhash.Sum([]byte("validators_hash")),
+			NextValidatorsHash: tmhash.Sum([]byte("next_validators_hash")),
+			ConsensusHash:      tmhash.Sum([]byte("consensus_hash")),
+			AppHash:            tmhash.Sum([]byte("app_hash")),
+			LastResultsHash:    tmhash.Sum([]byte("last_results_hash")),
+			EvidenceHash:       tmhash.Sum([]byte("evidence_hash")),
+			ProposerAddress:    crypto.AddressHash([]byte("proposer_address")),
+		}, hexBytesFromString("A37A7A69D89D3A66D599B0914A53F959EFE490EE9B449C95852F6FB331D58D07")},
+		{"nil header yields nil", nil, nil},
+		{"nil ValidatorsHash yields nil", &Header{
+			Version:            version.Consensus{Block: 1, App: 2},
+			ChainID:            "chainId",
+			Height:             3,
+			Time:               time.Date(2019, 10, 13, 16, 14, 44, 0, time.UTC),
+			NumTxs:             4,
+			TotalTxs:           5,
+			LastBlockID:        makeBlockID(make([]byte, tmhash.Size), 6, make([]byte, tmhash.Size)),
+			LastCommitHash:     tmhash.Sum([]byte("last_commit_hash")),
+			DataHash:           tmhash.Sum([]byte("data_hash")),
+			ValidatorsHash:     nil,
+			NextValidatorsHash: tmhash.Sum([]byte("next_validators_hash")),
+			ConsensusHash:      tmhash.Sum([]byte("consensus_hash")),
+			AppHash:            tmhash.Sum([]byte("app_hash")),
+			LastResultsHash:    tmhash.Sum([]byte("last_results_hash")),
+			EvidenceHash:       tmhash.Sum([]byte("evidence_hash")),
+			ProposerAddress:    crypto.AddressHash([]byte("proposer_address")),
+		}, nil},
+	}
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.desc, func(t *testing.T) {
+			assert.Equal(t, tc.expectHash, tc.header.Hash())
+
+			// We also make sure that all fields are hashed in struct order, and that all
+			// fields in the test struct are non-zero.
+			if tc.header != nil && tc.expectHash != nil {
+				byteSlices := [][]byte{}
+				s := reflect.ValueOf(*tc.header)
+				for i := 0; i < s.NumField(); i++ {
+					f := s.Field(i)
+					assert.False(t, f.IsZero(), "Found zero-valued field %v",
+						s.Type().Field(i).Name)
+					byteSlices = append(byteSlices, cdcEncode(f.Interface()))
+				}
+				assert.Equal(t,
+					cmn.HexBytes(merkle.SimpleHashFromByteSlices(byteSlices)), tc.header.Hash())
+			}
+		})
+	}
+}
+
 func TestMaxHeaderBytes(t *testing.T) {
 	// Construct a UTF-8 string of MaxChainIDLen length using the supplementary
 	// characters.
@@ -290,6 +360,14 @@ func randCommit() *Commit {
 	return commit
 }
 
+func hexBytesFromString(s string) cmn.HexBytes {
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		panic(err)
+	}
+	return cmn.HexBytes(b)
+}
+
 func TestBlockMaxDataBytes(t *testing.T) {
 	testCases := []struct {
 		maxBytes      int64