Adds a test to cover the last missing line in codecov for answer creation errors

resolver/custom_dns_resolver.go

@@ -18,6 +18,7 @@ import (
 // CustomDNSResolver resolves passed domain name to ip address defined in domain-IP map
 type CustomDNSResolver struct {
 	configurable[*config.CustomDNS]
+	CreateAnswerFromQuestion func(question dns.Question, ip net.IP, ttl uint32) (dns.RR, error)
 	NextResolver
 	typed
 
@@ -51,8 +52,9 @@ func NewCustomDNSResolver(cfg config.CustomDNS) *CustomDNSResolver {
 	}
 
 	return &CustomDNSResolver{
-		configurable: withConfig(&cfg),
-		typed:        withType("custom_dns"),
+		configurable:             withConfig(&cfg),
+		CreateAnswerFromQuestion: util.CreateAnswerFromQuestion,
+		typed:                    withType("custom_dns"),
 
 		mapping:          m,
 		reverseAddresses: reverse,
@@ -186,7 +188,7 @@ func (r *CustomDNSResolver) processIP(ip net.IP, question dns.Question) (result
 	result = make([]dns.RR, 0)
 
 	if isSupportedType(ip, question) {
-		rr, err := util.CreateAnswerFromQuestion(question, ip, r.cfg.CustomTTL.SecondsU32())
+		rr, err := r.CreateAnswerFromQuestion(question, ip, r.cfg.CustomTTL.SecondsU32())
 		if err != nil {
 			return nil, err
 		}

resolver/custom_dns_resolver_test.go

@@ -91,7 +91,20 @@ var _ = Describe("CustomDNSResolver", func() {
 				Expect(err.Error()).Should(ContainSubstring("context canceled"))
 			})
 		})
+		When("Creating the IP response returns an error ", func() {
+			It("should return the error", func() {
+				createAnswerMock := func(_ dns.Question, _ net.IP, _ uint32) (dns.RR, error) {
+					return nil, fmt.Errorf("create answer error")
+				}
 
+				sut.CreateAnswerFromQuestion = createAnswerMock
+
+				_, err := sut.Resolve(ctx, newRequest("custom.domain.", A))
+
+				Expect(err).Should(HaveOccurred())
+				Expect(err.Error()).Should(ContainSubstring("create answer error"))
+			})
+		})
 		When("The forward request returns an error ", func() {
 			It("should return the error if the error occurs when checking ipv4 forward addresses", func() {
 				err := fmt.Errorf("forward error")