Add support for using an extant MongoDB instance for mongodb_instance…

… fixture. Fixes #22.

CHANGES.rst

@@ -1,3 +1,11 @@
+v11.1.0
+=======
+
+#22: The pytest fixture now honors ``--mongodb-uri`` or
+the environment variable ``MONGODB_URL`` to run tests
+against an existing instance of MongoDB rather than starting
+up a new one.
+
 v11.0.1
 =======
 

jaraco/mongodb/fixtures.py

@@ -1,6 +1,7 @@
 # coding: future-fstrings
 
 import shlex
+import os
 
 import pytest
 
@@ -17,14 +18,30 @@ def pytest_addoption(parser):
         '--mongod-args',
         help="Arbitrary arguments to mongod",
     )
+    parser.addoption(
+        '--mongodb-uri',
+        help="URI to an extant MongoDB instance (supersedes ephemeral)",
+    )
 
 
 @pytest.yield_fixture(scope='session')
 def mongodb_instance(request):
     if 'pymongo' not in globals():
         pytest.skip("pymongo not available")
 
-    params_raw = request.config.getoption('mongod_args') or ''
+    yield from _extant_instance(request.config)
+    yield from _ephemeral_instance(request.config)
+
+
+def _extant_instance(config):
+    uri = config.getoption('mongodb_uri') or os.environ.get('MONGODB_URL')
+    if not uri:
+        return
+    yield service.ExtantInstance(uri)
+
+
+def _ephemeral_instance(config):
+    params_raw = config.getoption('mongod_args') or ''
     params = shlex.split(params_raw)
     try:
         instance = service.MongoDBInstance()

jaraco/mongodb/service.py

@@ -140,6 +140,18 @@ def stop(self):
         del self.data_dir
 
 
+class ExtantInstance:
+    def __init__(self, uri):
+        self.uri = uri
+
+    def get_connection(self):
+        pymongo = importlib.import_module('pymongo')
+        return pymongo.MongoClient(self.uri)
+
+    def get_uri(self):
+        return self.uri
+
+
 class MongoDBReplicaSet(MongoDBFinder, services.Service):
     replica_set_name = 'test'