Validate exact expected error in signed header verification tests (#1165)

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## Overview
Closes: #1049

Stacked on top of #1162

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## Checklist

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- [x] New and updated code has appropriate documentation
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---------

Co-authored-by: Matthew Sevey <mjsevey@gmail.com>

Author: Manav-Aggarwal

types/header.go

@@ -2,7 +2,6 @@ package types
 
 import (
 	"encoding"
-	"errors"
 	"fmt"
 	"time"
 
@@ -85,7 +84,7 @@ func (h *Header) Verify(untrst header.Header) error {
 	}
 	// sanity check fields
 	if err := verifyNewHeaderAndVals(h, untrstH); err != nil {
-		return &header.VerifyError{Reason: err}
+		return err
 	}
 
 	// Check the validator hashes are the same in the case headers are adjacent
@@ -132,16 +131,22 @@ func verifyNewHeaderAndVals(trusted, untrusted *Header) error {
 	}
 
 	if !untrusted.Time().After(trusted.Time()) {
-		return fmt.Errorf("expected new header time %v to be after old header time %v",
-			untrusted.Time(),
-			trusted.Time())
+		return fmt.Errorf("%w: %w",
+			ErrNewHeaderTimeBeforeOldHeaderTime,
+			fmt.Errorf("expected new header time %v to be after %v",
+				untrusted.Time(),
+				trusted.Time(),
+			),
+		)
 	}
 
 	if !untrusted.Time().Before(time.Now().Add(maxClockDrift)) {
-		return fmt.Errorf("new header has a time from the future %v (now: %v; max clock drift: %v)",
+		return fmt.Errorf("%w: new header time %v (now: %v; max clock drift: %v)",
+			ErrNewHeaderTimeFromFuture,
 			untrusted.Time(),
 			time.Now(),
-			maxClockDrift)
+			maxClockDrift,
+		)
 	}
 
 	return nil
@@ -150,7 +155,7 @@ func verifyNewHeaderAndVals(trusted, untrusted *Header) error {
 // ValidateBasic performs basic validation of a header.
 func (h *Header) ValidateBasic() error {
 	if len(h.ProposerAddress) == 0 {
-		return errors.New("no proposer address")
+		return ErrNoProposerAddress
 	}
 
 	return nil

types/signed_header.go

@@ -17,6 +17,16 @@ func (sH *SignedHeader) IsZero() bool {
 	return sH == nil
 }
 
+var (
+	ErrAggregatorSetHashMismatch        = errors.New("aggregator set hash in signed header and hash of validator set do not match")
+	ErrSignatureVerificationFailed      = errors.New("signature verification failed")
+	ErrNoProposerAddress                = errors.New("no proposer address")
+	ErrLastHeaderHashMismatch           = errors.New("last header hash mismatch")
+	ErrLastCommitHashMismatch           = errors.New("last commit hash mismatch")
+	ErrNewHeaderTimeBeforeOldHeaderTime = errors.New("new header has time before old header time")
+	ErrNewHeaderTimeFromFuture          = errors.New("new header has time from future")
+)
+
 func (sH *SignedHeader) Verify(untrst header.Header) error {
 	// Explicit type checks are required due to embedded Header which also does the explicit type check
 	untrstH, ok := untrst.(*SignedHeader)
@@ -44,13 +54,19 @@ func (sH *SignedHeader) Verify(untrst header.Header) error {
 	sHHash := sH.Header.Hash()
 	if !bytes.Equal(untrstH.LastHeaderHash[:], sHHash) {
 		return &header.VerifyError{
-			Reason: fmt.Errorf("last header hash %v does not match hash of previous header %v", untrstH.LastHeaderHash[:], sHHash),
+			Reason: fmt.Errorf("%w: expected %v, but got %v",
+				ErrLastHeaderHashMismatch,
+				untrstH.LastHeaderHash[:], sHHash,
+			),
 		}
 	}
 	sHLastCommitHash := sH.Commit.GetCommitHash(&untrstH.Header, sH.ProposerAddress)
 	if !bytes.Equal(untrstH.LastCommitHash[:], sHLastCommitHash) {
 		return &header.VerifyError{
-			Reason: fmt.Errorf("last commit hash %v does not match hash of previous header %v", untrstH.LastCommitHash[:], sHHash),
+			Reason: fmt.Errorf("%w: expected %v, but got %v",
+				ErrLastCommitHashMismatch,
+				untrstH.LastCommitHash[:], sHHash,
+			),
 		}
 	}
 	return nil
@@ -78,7 +94,7 @@ func (h *SignedHeader) ValidateBasic() error {
 	}
 
 	if !bytes.Equal(h.Validators.Hash(), h.AggregatorsHash[:]) {
-		return errors.New("aggregator set hash in signed header and hash of validator set do not match")
+		return ErrAggregatorSetHashMismatch
 	}
 
 	// Make sure there is exactly one signature
@@ -94,7 +110,7 @@ func (h *SignedHeader) ValidateBasic() error {
 		return errors.New("signature verification failed, unable to marshal header")
 	}
 	if !pubKey.VerifySignature(msg, signature) {
-		return errors.New("signature verification failed")
+		return ErrSignatureVerificationFailed
 	}
 
 	return nil

types/signed_header_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/celestiaorg/go-header"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -15,37 +16,46 @@ func TestVerify(t *testing.T) {
 	time.Sleep(time.Second)
 	untrustedAdj, err := GetNextRandomHeader(trusted, privKey)
 	require.NoError(t, err)
+	fakeAggregatorsHash := header.Hash(GetRandomBytes(32))
+	fakeLastHeaderHash := header.Hash(GetRandomBytes(32))
+	fakeLastCommitHash := header.Hash(GetRandomBytes(32))
 	tests := []struct {
 		prepare func() (*SignedHeader, bool)
-		err     bool
+		err     error
 	}{
 		{
 			prepare: func() (*SignedHeader, bool) { return untrustedAdj, false },
-			err:     false,
+			err:     nil,
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
-				untrusted.AggregatorsHash = GetRandomBytes(32)
-				return &untrusted, true
+				untrusted.AggregatorsHash = fakeAggregatorsHash
+				return &untrusted, false
+			},
+			err: &header.VerifyError{
+				Reason: ErrAggregatorSetHashMismatch,
 			},
-			err: true,
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
-				untrusted.LastHeaderHash = GetRandomBytes(32)
+				untrusted.LastHeaderHash = fakeLastHeaderHash
 				return &untrusted, true
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrLastHeaderHashMismatch,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
-				untrusted.LastCommitHash = GetRandomBytes(32)
+				untrusted.LastCommitHash = fakeLastCommitHash
 				return &untrusted, true
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrLastCommitHashMismatch,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
@@ -54,47 +64,57 @@ func TestVerify(t *testing.T) {
 				untrusted.Header.BaseHeader.Height++
 				return &untrusted, true
 			},
-			err: false, // Accepts non-adjacent headers
+			err: nil, // Accepts non-adjacent headers
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
 				untrusted.Header.BaseHeader.Time = uint64(untrusted.Header.Time().Truncate(time.Hour).UnixNano())
 				return &untrusted, true
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrNewHeaderTimeBeforeOldHeaderTime,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
 				untrusted.Header.BaseHeader.Time = uint64(untrusted.Header.Time().Add(time.Minute).UnixNano())
 				return &untrusted, true
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrNewHeaderTimeFromFuture,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
 				untrusted.BaseHeader.ChainID = "toaster"
 				return &untrusted, false // Signature verification should fail
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrSignatureVerificationFailed,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
 				untrusted.Version.App = untrusted.Version.App + 1
 				return &untrusted, false // Signature verification should fail
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrSignatureVerificationFailed,
+			},
 		},
 		{
 			prepare: func() (*SignedHeader, bool) {
 				untrusted := *untrustedAdj
 				untrusted.ProposerAddress = nil
 				return &untrusted, true
 			},
-			err: true,
+			err: &header.VerifyError{
+				Reason: ErrNoProposerAddress,
+			},
 		},
 	}
 
@@ -107,11 +127,17 @@ func TestVerify(t *testing.T) {
 				preparedHeader.Commit = *commit
 			}
 			err = trusted.Verify(preparedHeader)
-			if test.err {
-				assert.Error(t, err)
-			} else {
+			if test.err == nil {
 				assert.NoError(t, err)
+				return
+			}
+			if err == nil {
+				t.Errorf("expected err: %v, got nil", test.err)
+				return
 			}
+			reason := err.(*header.VerifyError).Reason
+			testReason := test.err.(*header.VerifyError).Reason
+			assert.ErrorIs(t, reason, testReason)
 		})
 	}
 }