Adding test cases for Corefile parsing (#193)

Adding test cases for Corefile parsing.
Some code refactoring to allow test reuse.

middleware/kubernetes/nametemplate/nametemplate.go

@@ -37,6 +37,11 @@ var types = []string{
 	"pod",
 }
 
+var requiredSymbols = []string{
+	"namespace",
+	"service",
+}
+
 // TODO: Validate that provided NameTemplate string only contains:
 //			* valid, known symbols, or
 //			* static strings
@@ -90,6 +95,12 @@ func (t *NameTemplate) SetTemplate(s string) error {
 		}
 	}
 
+	if err == nil && !t.IsValid() {
+		err = errors.New("Record name template does not pass NameTemplate validation")
+		log.Printf("[debug] %v\n", err)
+		return err
+	}
+
 	return err
 }
 
@@ -157,6 +168,20 @@ func (t *NameTemplate) GetRecordNameFromNameValues(values NameValues) string {
 	return strings.Join(recordName, ".")
 }
 
+func (t *NameTemplate) IsValid() bool {
+	result := true
+
+	// Ensure that all requiredSymbols are found in NameTemplate
+	for _, symbol := range requiredSymbols {
+		if _, ok := t.Element[symbol]; !ok {
+			result = false
+			break
+		}
+	}
+
+	return result
+}
+
 type NameValues struct {
 	ServiceName string
 	Namespace   string