Improve code coverage with a domain that returns NOANSWER instead of NXDOMAIN

Author: JoshData

tests/mocked-dns-answers.json

@@ -60,6 +60,30 @@
    "\"v=spf1 -all\""
   ]
  },
+ {
+  "query": {
+   "name": "justtxt.joshdata.me",
+   "type": "MX",
+   "class": "IN"
+  },
+  "answer": []
+ },
+ {
+  "query": {
+   "name": "justtxt.joshdata.me",
+   "type": "A",
+   "class": "IN"
+  },
+  "answer": []
+ },
+ {
+  "query": {
+   "name": "justtxt.joshdata.me",
+   "type": "AAAA",
+   "class": "IN"
+  },
+  "answer": []
+ },
  {
   "query": {
    "name": "mail.example",

tests/test_deliverability.py

@@ -21,7 +21,7 @@ def test_deliverability_found():
 
 
 def test_deliverability_fails():
-    # No MX record.
+    # Domain does not exist.
     domain = 'xkxufoekjvjfjeodlfmdfjcu.com'
     with pytest.raises(EmailUndeliverableError, match=f'The domain name {domain} does not exist'):
         validate_email_deliverability(domain, domain, dns_resolver=RESOLVER)
@@ -36,6 +36,12 @@ def test_deliverability_fails():
     with pytest.raises(EmailUndeliverableError, match=f'The domain name {domain} does not send email'):
         validate_email_deliverability(domain, domain, dns_resolver=RESOLVER)
 
+    # No MX or A/AAAA records, but some other DNS records must
+    # exist such that the response is NOANSWER instead of NXDOMAIN.
+    domain = 'justtxt.joshdata.me'
+    with pytest.raises(EmailUndeliverableError, match=f'The domain name {domain} does not accept email'):
+        validate_email_deliverability(domain, domain, dns_resolver=RESOLVER)
+
 
 @pytest.mark.parametrize(
     'email_input',