Add tests about the RuntimeError issue

when HTTPretty.enable(), we should contine to do DNS query,
like it's done in the
test_httpretty_should_not_raise_on_socket_send_when_uri_not_registered
test.

The test test_httpretty_should_raise_on_socket_send_when_uri_registered
is written to check that the RuntimeError is still raised when
the port is used for http traffic.

tests/unit/test_httpretty.py

@@ -26,7 +26,7 @@
 # OTHER DEALINGS IN THE SOFTWARE.
 from __future__ import unicode_literals
 from sure import expect
-from httpretty import HTTPretty, HTTPrettyError
+from httpretty import HTTPretty, HTTPrettyError, core
 from httpretty.core import URIInfo, BaseClass, Entry, FakeSockFile
 from httpretty.http import STATUSES
 
@@ -53,6 +53,47 @@ def test_httpretty_should_raise_proper_exception_on_inconsistent_length():
     )
 
 
+def test_httpretty_should_raise_on_socket_send_when_uri_registered():
+    """HTTPretty should raise a RuntimeError when the fakesocket is used in
+    an invalid usage.
+    """
+    import socket
+    HTTPretty.enable()
+
+    defaults = core.POTENTIAL_HTTP_PORTS[:]
+    HTTPretty.register_uri(HTTPretty.GET,
+                           'http://127.0.0.1:5000')
+    expect(core.POTENTIAL_HTTP_PORTS).to.be.equal([80, 443, 5000])
+
+    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    sock.connect(('127.0.0.1', 5000))
+    expect(sock.send).when.called_with('whatever').to.throw(RuntimeError)
+    sock.close()
+
+    # restore the previous value
+    core.POTENTIAL_HTTP_PORTS = defaults
+    HTTPretty.reset()
+    HTTPretty.disable()
+
+
+def test_httpretty_should_not_raise_on_socket_send_when_uri_not_registered():
+    """HTTPretty should not raise a RuntimeError when the fakesocket is used in
+    an invalid usage.
+    """
+    import socket
+    HTTPretty.enable()
+
+    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0)
+    sock.setblocking(0)
+    expect(sock.sendto).when.called_with('whatever',
+                                         ('127.0.0.1', 53)
+                                         ).should_not.throw(RuntimeError)
+
+    sock.close()
+    HTTPretty.reset()
+    HTTPretty.disable()
+
+
 def test_does_not_have_last_request_by_default():
     'HTTPretty.last_request is a dummy object by default'
     HTTPretty.reset()