plugin/cache: add extra test for FORMERR (#1930)

* plugin/cache: add extra test for FORMERR

Add extra test that test for not caching a formerr.
Signed-off-by: Miek Gieben <miek@miek.nl>

* govet
Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/cache/error_test.go

+package cache
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestFormErr(t *testing.T) {
+	c := New()
+	c.Next = formErrHandler()
+
+	req := new(dns.Msg)
+	req.SetQuestion("example.org.", dns.TypeA)
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+
+	c.ServeDNS(context.TODO(), rec, req)
+
+	if c.pcache.Len() != 0 {
+		t.Errorf("Cached %s, while reply had %d", "example.org.", rec.Msg.Rcode)
+	}
+}
+
+// formErrHanlder is a fake plugin implementation which returns a FORMERR for a reply.
+func formErrHandler() plugin.Handler {
+	return plugin.HandlerFunc(func(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+		m := new(dns.Msg)
+		m.SetQuestion("example.net.", dns.TypeA)
+		m.Rcode = dns.RcodeFormatError
+		w.WriteMsg(m)
+		return dns.RcodeSuccess, nil
+	})
+}

plugin/cache/spoof_test.go

@@ -6,8 +6,8 @@ import (
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
-
 	"github.com/coredns/coredns/plugin/test"
+
 	"github.com/miekg/dns"
 )