make errors more easily checkable

Author: whyrusleeping

ipld.go

@@ -66,6 +66,11 @@ func (se SerializationError) Unwrap() error {
 	return se.err
 }
 
+func (se SerializationError) Is(o error) bool {
+	_, ok := o.(*SerializationError)
+	return ok
+}
+
 type blocks interface {
 	GetBlock(context.Context, cid.Cid) (block.Block, error)
 	AddBlock(block.Block) error

ipld_test.go

@@ -3,9 +3,11 @@ package hamt
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"testing"
 
 	cbg "github.com/whyrusleeping/cbor-gen"
+	xerrors "golang.org/x/xerrors"
 
 	cbor "github.com/ipfs/go-ipld-cbor"
 )
@@ -58,3 +60,11 @@ func TestBasicBytesLoading(t *testing.T) {
 		t.Fatal("bytes round trip failed")
 	}
 }
+
+func TestIsSerializationError(t *testing.T) {
+	serr := NewSerializationError(fmt.Errorf("i am a cat"))
+
+	if !xerrors.Is(serr, &SerializationError{}) {
+		t.Fatal("its not a serialization error?")
+	}
+}