diff --git a/src/rez/plugin_managers.py b/src/rez/plugin_managers.py
index 20ce8a873..dbcab4eb8 100644
--- a/src/rez/plugin_managers.py
+++ b/src/rez/plugin_managers.py
@@ -73,6 +73,11 @@ def append_if_valid(dir_):
     return path
 
 
+def uncache_sys_module_paths(instance=None):
+    instance = instance or plugin_manager
+    cached_property.uncache(instance, "sys_module_paths")
+
+
 class RezPluginType(object):
     """An abstract base class representing a single type of plugin.
 
diff --git a/src/rez/tests/data/extensions/bar/__init__.py b/src/rez/tests/data/extensions/bar/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/bar/rezplugins/__init__.py b/src/rez/tests/data/extensions/bar/rezplugins/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/bar/rezplugins/package_repository/__init__.py b/src/rez/tests/data/extensions/bar/rezplugins/package_repository/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/bar/rezplugins/package_repository/memory.py b/src/rez/tests/data/extensions/bar/rezplugins/package_repository/memory.py
new file mode 100644
index 000000000..4a0a72437
--- /dev/null
+++ b/src/rez/tests/data/extensions/bar/rezplugins/package_repository/memory.py
@@ -0,0 +1,13 @@
+
+from rez.package_repository import PackageRepository
+
+
+class MemoryPackageRepository(PackageRepository):
+    @classmethod
+    def name(cls):
+        return "memory"
+    on_test = "bar"
+
+
+def register_plugin():
+    return MemoryPackageRepository
diff --git a/src/rez/tests/data/extensions/foo/__init__.py b/src/rez/tests/data/extensions/foo/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/foo/rezplugins/__init__.py b/src/rez/tests/data/extensions/foo/rezplugins/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/foo/rezplugins/package_repository/__init__.py b/src/rez/tests/data/extensions/foo/rezplugins/package_repository/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/foo/rezplugins/package_repository/cloud.py b/src/rez/tests/data/extensions/foo/rezplugins/package_repository/cloud.py
new file mode 100644
index 000000000..f5729a185
--- /dev/null
+++ b/src/rez/tests/data/extensions/foo/rezplugins/package_repository/cloud.py
@@ -0,0 +1,12 @@
+
+from rez.package_repository import PackageRepository
+
+
+class CloudPackageRepository(PackageRepository):
+    @classmethod
+    def name(cls):
+        return "cloud"
+
+
+def register_plugin():
+    return CloudPackageRepository
diff --git a/src/rez/tests/data/extensions/non-mod/rezplugins/__init__.py b/src/rez/tests/data/extensions/non-mod/rezplugins/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/non-mod/rezplugins/package_repository/__init__.py b/src/rez/tests/data/extensions/non-mod/rezplugins/package_repository/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/rez/tests/data/extensions/non-mod/rezplugins/package_repository/memory.py b/src/rez/tests/data/extensions/non-mod/rezplugins/package_repository/memory.py
new file mode 100644
index 000000000..263081007
--- /dev/null
+++ b/src/rez/tests/data/extensions/non-mod/rezplugins/package_repository/memory.py
@@ -0,0 +1,13 @@
+
+from rez.package_repository import PackageRepository
+
+
+class MemoryPackageRepository(PackageRepository):
+    @classmethod
+    def name(cls):
+        return "memory"
+    on_test = "non-mod"
+
+
+def register_plugin():
+    return MemoryPackageRepository
diff --git a/src/rez/tests/test_plugin_manager.py b/src/rez/tests/test_plugin_manager.py
new file mode 100644
index 000000000..a5a73d99f
--- /dev/null
+++ b/src/rez/tests/test_plugin_manager.py
@@ -0,0 +1,112 @@
+"""
+test rezplugins manager behaviors
+"""
+from rez.tests.util import TestBase, TempdirMixin, restore_sys_path
+from rez.plugin_managers import (
+    uncache_sys_module_paths,
+    RezPluginManager,
+    ShellPluginType,
+    ReleaseVCSPluginType,
+    ReleaseHookPluginType,
+    BuildSystemPluginType,
+    PackageRepositoryPluginType,
+    BuildProcessPluginType,
+    CommandPluginType
+)
+import os
+import sys
+import unittest
+
+
+class TestPluginManagers(TestBase, TempdirMixin):
+    def __init__(self, *nargs, **kwargs):
+        TestBase.__init__(self, *nargs, **kwargs)
+        self._original_modules = set()
+        self.plugin_manager = None
+
+    def setUp(self):
+        TestBase.setUp(self)
+        uncache_sys_module_paths()
+
+        plugin_manager = RezPluginManager()
+        plugin_manager.register_plugin_type(ShellPluginType)
+        plugin_manager.register_plugin_type(ReleaseVCSPluginType)
+        plugin_manager.register_plugin_type(ReleaseHookPluginType)
+        plugin_manager.register_plugin_type(BuildSystemPluginType)
+        plugin_manager.register_plugin_type(PackageRepositoryPluginType)
+        plugin_manager.register_plugin_type(BuildProcessPluginType)
+        plugin_manager.register_plugin_type(CommandPluginType)
+
+        self._original_modules.update(sys.modules.keys())
+        self.plugin_manager = plugin_manager
+
+    def tearDown(self):
+        TestBase.tearDown(self)
+        self.plugin_manager = None
+
+        for key in set(sys.modules.keys()):
+            if key not in self._original_modules:
+                del sys.modules[key]
+        self._original_modules.clear()
+
+    def test_old_loading_style(self):
+        """Test loading rez plugin from plugin_path"""
+        path = os.path.realpath(os.path.dirname(__file__))
+        self.update_settings(dict(
+            plugin_path=[os.path.join(path, "data", "extensions", "foo")]
+        ))
+
+        cloud_cls = self.plugin_manager.get_plugin_class(
+            "package_repository", "cloud")
+        self.assertEqual(cloud_cls.name(), "cloud")
+
+    def test_new_loading_style(self):
+        """Test loading rez plugin from python modules"""
+        path = os.path.realpath(os.path.dirname(__file__))
+        with restore_sys_path():
+            sys.path.append(os.path.join(path, "data", "extensions"))
+
+            cloud_cls = self.plugin_manager.get_plugin_class(
+                "package_repository", "cloud")
+            self.assertEqual(cloud_cls.name(), "cloud")
+
+    def test_plugin_override_1(self):
+        """Test plugin from plugin_path can override the default"""
+        path = os.path.realpath(os.path.dirname(__file__))
+        self.update_settings(dict(
+            plugin_path=[os.path.join(path, "data", "extensions", "non-mod")]
+        ))
+
+        mem_cls = self.plugin_manager.get_plugin_class(
+            "package_repository", "memory")
+        self.assertEqual("non-mod", mem_cls.on_test)
+
+    def test_plugin_override_2(self):
+        """Test plugin from python modules can override the default"""
+        path = os.path.realpath(os.path.dirname(__file__))
+        with restore_sys_path():
+            sys.path.append(os.path.join(path, "data", "extensions"))
+
+            mem_cls = self.plugin_manager.get_plugin_class(
+                "package_repository", "memory")
+            self.assertEqual("bar", mem_cls.on_test)
+
+    def test_plugin_override_3(self):
+        """Test plugin from python modules can override plugin_path"""
+        path = os.path.realpath(os.path.dirname(__file__))
+        with restore_sys_path():
+            # setup new
+            sys.path.append(os.path.join(path, "data", "extensions"))
+            # setup old
+            self.update_settings(dict(
+                plugin_path=[os.path.join(path, "data", "extensions", "non-mod")]
+            ))
+
+            mem_cls = self.plugin_manager.get_plugin_class(
+                "package_repository", "memory")
+            self.assertEqual("bar", mem_cls.on_test)
+
+
+if __name__ == '__main__':
+    unittest.main()
+