PYTHON-2762 Avoid duplicating unified test files for LB testing (#649)

Create new client for each cursor/session __del__ test.
Always close cursors in spec tests.

(cherry picked from commit b4b7a07)

Author: ShaneHarvey

.evergreen/run-tests.sh

@@ -225,19 +225,8 @@ if [ -z "$GREEN_FRAMEWORK" ]; then
         # causing this script to exit.
         $PYTHON -c "from bson import _cbson; from pymongo import _cmessage"
     fi
-    if [ -n "$TEST_LOADBALANCER" ]; then
-        IS_PRE_35=$(python -c "import sys; sys.stdout.write('1' if sys.version_info < (3, 5) else '0')")
-        if [ "$IS_PRE_35" = "1" ]; then
-            RUNNER="unittest"
-            RUNNER_ARGS=""
-        else
-            RUNNER="xmlrunner"
-            RUNNER_ARGS="--locals -o $XUNIT_DIR"
-        fi
-        $COVERAGE_OR_PYTHON $PYTHON_ARGS $COVERAGE_ARGS -m $RUNNER discover $RUNNER_ARGS -s test/load_balancer -v
-    else
-        $COVERAGE_OR_PYTHON $PYTHON_ARGS $COVERAGE_ARGS setup.py $C_EXTENSIONS test $TEST_ARGS $OUTPUT
-    fi
+
+    $PYTHON $COVERAGE_ARGS setup.py $C_EXTENSIONS test $TEST_ARGS $OUTPUT
 else
     # --no_ext has to come before "test" so there is no way to toggle extensions here.
     $PYTHON green_framework_test.py $GREEN_FRAMEWORK $OUTPUT

test/__init__.py

@@ -578,6 +578,24 @@ def sec_count():
         return self._require(lambda: sec_count() >= count,
                              "Not enough secondaries available")
 
+    @property
+    def supports_secondary_read_pref(self):
+        if self.has_secondaries:
+            return True
+        if self.is_mongos:
+            shard = self.client.config.shards.find_one()['host']
+            num_members = shard.count(',') + 1
+            return num_members > 1
+        return False
+
+    def require_secondary_read_pref(self):
+        """Run a test only if the client is connected to a cluster that
+        supports secondary read preference
+        """
+        return self._require(lambda: self.supports_secondary_read_pref,
+                             "This cluster does not support secondary read "
+                             "preference")
+
     def require_no_replica_set(self, func):
         """Run a test if the client is *not* connected to a replica set."""
         return self._require(
@@ -628,6 +646,13 @@ def require_load_balancer(self, func):
                              "Must be connected to a load balancer",
                              func=func)
 
+    def require_no_load_balancer(self, func):
+        """Run a test only if the client is not connected to a load balancer.
+        """
+        return self._require(lambda: not self.load_balancer,
+                             "Must not be connected to a load balancer",
+                             func=func)
+
     def check_auth_with_sharding(self, func):
         """Skip a test when connected to mongos < 2.0 and running with auth."""
         condition = lambda: not (self.auth_enabled and
@@ -838,6 +863,9 @@ class IntegrationTest(PyMongoTestCase):
     @classmethod
     @client_context.require_connection
     def setUpClass(cls):
+        if (client_context.load_balancer and
+                not getattr(cls, 'RUN_ON_LOAD_BALANCER', False)):
+            raise SkipTest('this test does not support load balancers')
         cls.client = client_context.client
         cls.db = cls.client.pymongo_test
         if client_context.auth_enabled:
@@ -861,6 +889,14 @@ class MockClientTest(unittest.TestCase):
     The class temporarily overrides HEARTBEAT_FREQUENCY to speed up tests.
     """
 
+    # MockClients tests that use replicaSet, directConnection=True, pass
+    # multiple seed addresses, or wait for heartbeat events are incompatible
+    # with loadBalanced=True.
+    @classmethod
+    @client_context.require_no_load_balancer
+    def setUpClass(cls):
+        pass
+
     def setUp(self):
         super(MockClientTest, self).setUp()