Proxy ErrAttributeNotFound from clib to allow consumers to test again…

…st the error

clib/clib.go

@@ -1684,7 +1684,7 @@ func XMLElementGetAttributeNode(n PtrSource, name string) (uintptr, error) {
 	}
 
 	if prop == nil || XMLNodeType(prop._type) != AttributeNode {
-		return 0, errors.New("attribute not found")
+		return 0, ErrAttributeNotFound
 	}
 
 	return uintptr(unsafe.Pointer(prop)), nil

clib/interface.go

@@ -54,6 +54,7 @@ const (
 )
 
 var (
+	ErrAttributeNotFound      = errors.New("attribute not found")
 	ErrAttributeNameTooLong   = errors.New("attribute name too long")
 	ErrElementNameTooLong     = errors.New("element name too long")
 	ErrNamespaceURITooLong    = errors.New("namespace uri too long")

dom/interface.go

@@ -7,7 +7,7 @@ import (
 )
 
 var (
-	ErrAttributeNotFound = errors.New("attribute not found")
+	ErrAttributeNotFound = clib.ErrAttributeNotFound
 	ErrInvalidNodeType   = errors.New("invalid node type")
 )
 

parser_test.go

@@ -4,6 +4,9 @@ import (
 	"regexp"
 	"testing"
 
+	"github.com/lestrrat/go-libxml2/dom"
+	"github.com/lestrrat/go-libxml2/types"
+
 	"github.com/lestrrat/go-libxml2/clib"
 	"github.com/lestrrat/go-libxml2/parser"
 	"github.com/stretchr/testify/assert"
@@ -330,3 +333,27 @@ func TestPiWrapNodeIssue(t *testing.T) {
 		t.Fatalf("XML did not convert back correctly, expected: %v, got: %v", textXML, str)
 	}
 }
+
+func TestGetNonexistentAttributeReturnsRecoverableError(t *testing.T) {
+	const src = `<?xml version="1.0"?><rootnode/>`
+	doc, err := ParseString(src)
+	if !assert.NoError(t, err, "Should parse") {
+		return
+	}
+	defer doc.Free()
+
+	rootNode, err := doc.DocumentElement()
+	if !assert.NoError(t, err, "Should find root element") {
+		return
+	}
+
+	el, ok := rootNode.(types.Element)
+	if !ok {
+		t.Fatalf("Root node was not an element")
+	}
+
+	_, err = el.GetAttribute("non-existant")
+	if err != dom.ErrAttributeNotFound {
+		t.Fatalf("GetAttribute() error not comparable to existing library")
+	}
+}