In tests, don't configure the dns.resolver.Resolver when using mocked DNS data

The mocked DNS response class, which allows tests to run without a live
Internet connection, creates a dns.resolver.Resolver that still tries to
be configured using /etc/resolve.conf. That fails when the file cannot be read.

When using mocked data, this is now disabled.

Fixes #127.

Author: JoshData

email_validator/deliverability.py

@@ -6,11 +6,11 @@
 import dns.exception
 
 
-def caching_resolver(*, timeout: Optional[int] = None, cache=None):
+def caching_resolver(*, timeout: Optional[int] = None, cache=None, dns_resolver=None):
     if timeout is None:
         from . import DEFAULT_TIMEOUT
         timeout = DEFAULT_TIMEOUT
-    resolver = dns.resolver.Resolver()
+    resolver = dns_resolver or dns.resolver.Resolver()
     resolver.cache = cache or dns.resolver.LRUCache()  # type: ignore
     resolver.lifetime = timeout  # type: ignore # timeout, in seconds
     return resolver

tests/mocked_dns_response.py

@@ -32,7 +32,8 @@ def create_resolver():
 
         # Return a new dns.resolver.Resolver configured for caching
         # using the singleton instance.
-        return caching_resolver(cache=MockedDnsResponseData.INSTANCE)
+        dns_resolver = dns.resolver.Resolver(configure=BUILD_MOCKED_DNS_RESPONSE_DATA)
+        return caching_resolver(cache=MockedDnsResponseData.INSTANCE, dns_resolver=dns_resolver)
 
     def __init__(self):
         self.data = {}