Fix comment on Decapsulate

interface.go

@@ -47,9 +47,9 @@ type Multiaddr interface {
 	//
 	Encapsulate(Multiaddr) Multiaddr
 
-	// Decapsultate removes a Multiaddr wrapping. For example:
+	// Decapsulate removes a Multiaddr wrapping. For example:
 	//
-	//      /ip4/1.2.3.4/tcp/80 decapsulate /ip4/1.2.3.4 = /tcp/80
+	//      /ip4/1.2.3.4/tcp/80 decapsulate /tcp/80 = /ip4/1.2.3.4
 	//
 	Decapsulate(Multiaddr) Multiaddr
 

multiaddr_test.go

@@ -427,6 +427,15 @@ func TestEncapsulate(t *testing.T) {
 	}
 }
 
+func TestDecapsulateComment(t *testing.T) {
+	// shows the behavior from the interface comment
+	m := StringCast("/ip4/1.2.3.4/tcp/80")
+	rest := m.Decapsulate(StringCast("/tcp/80"))
+	if rest.String() != "/ip4/1.2.3.4" {
+		t.Fatalf("Documented behavior is not correct. Expected %v saw %v", "/ip4/1.2.3.4/", rest.String())
+	}
+}
+
 func assertValueForProto(t *testing.T, a Multiaddr, p int, exp string) {
 	t.Logf("checking for %s in %s", ProtocolWithCode(p).Name, a)
 	fv, err := a.ValueForProtocol(p)