diff --git a/gapstring/gapstring_test.go b/gapstring/gapstring_test.go
index d14d69e..d9c0bf2 100644
--- a/gapstring/gapstring_test.go
+++ b/gapstring/gapstring_test.go
@@ -5,7 +5,7 @@ import (
 	"testing"
 )
 
-func assertEqual(name string, a, b interface{}, t *testing.T) {
+func assertEqual(t *testing.T, name string, a, b interface{}) {
 	if a != b {
 		t.Errorf("%s: %#v != %#v", name, a, b)
 	}
@@ -15,11 +15,11 @@ func TestChunk(t *testing.T) {
 	var c chunk
 	
 	c = chunk{gap: 2}
-	assertEqual("gap chunk", c.length(), 2, t)
+	assertEqual(t, "gap chunk", c.length(), 2)
 	
 	c = chunk{data: []byte("moo")}
-	assertEqual("byte chunk", c.length(), 3, t)
-	assertEqual("byte slice", string(c.slice(1,3).data), "oo", t)
+	assertEqual(t, "byte chunk", c.length(), 3)
+	assertEqual(t, "byte slice", string(c.slice(1,3).data), "oo")
 }
 
 func TestGapString(t *testing.T) {
@@ -59,18 +59,18 @@ func TestGapString(t *testing.T) {
 	}
 	
 	g = g.AppendString("baz")
-	if g.String("") != "moobarbaz" {
-		t.Errorf("String conversion with empty string")
-	}
-	if g.String("DROP") != "moobarOPDROPDRbaz" {
-		t.Errorf("String conversion with fill")
-	}
+	assertEqual(t, "string", g.String(""), "moobarbaz")
+	assertEqual(t, "string drop", g.String("DROP"), "moobarOPDROPDRbaz")
+
+	assertEqual(t, "xor", g.Xor(1).String(""), "lnnc`sc`{")
+	assertEqual(t, "xor drop", g.Xor(1).String("DROP"), "lnnc`sOPDROPDRc`{")
 	
-	assertEqual("slice", g.Slice(2, 5).String(""), "oba", t)
+	assertEqual(t, "slice", g.Slice(2, 5).String(""), "oba")
+	assertEqual(t, "slice+xor", g.Slice(2, 5).Xor(1).String(""), "nc`")
 
 	hexdump :=
 		"00000000  6d 6f 6f 62 61 72 -- --  -- -- -- -- -- -- 62 61  moobar��������ba\n" +
 		"00000010  7a                                                z\n" +
 		"00000011\n"
-	assertEqual("hexdump", g.Hexdump(), hexdump, t)
+	assertEqual(t, "hexdump", g.Hexdump(), hexdump)
 }