tests: clean up output

Some document improvements and add a few more tests.

middleware/pkg/rcode/rcode_test.go

@@ -0,0 +1,29 @@
+package rcode
+
+import (
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestToString(t *testing.T) {
+	tests := []struct {
+		in       int
+		expected string
+	}{
+		{
+			dns.RcodeSuccess,
+			"NOERROR",
+		},
+		{
+			28,
+			"RCODE28",
+		},
+	}
+	for i, test := range tests {
+		got := ToString(test.in)
+		if got != test.expected {
+			t.Errorf("Test %d, expected %s, got %s", i, test.expected, got)
+		}
+	}
+}