[core] Plugins: Introduction of NodePluginManager

The NodePluginManager provides a way for registering and managing node plugins within Meshroom. This also provides a way for other components to interact with the plugins to understand whether a plugin is available or not.

tests/test_plugins.py

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+""" Test for Meshroom Plugins.
+"""
+#!/usr/bin/env python
+# coding:utf-8
+
+from meshroom.core import _plugins
+from meshroom.core import desc, registerNodeType, unregisterNodeType
+
+
+class SampleNode(desc.Node):
+    """ Sample Node for unit testing """
+
+    category = "Sample"
+
+    inputs = [
+        desc.File(name='input', label='Input', description='', value='',),
+        desc.StringParam(name='paramA', label='ParamA', description='', value='', invalidate=False)  # No impact on UID
+    ]
+    outputs = [
+        desc.File(name='output', label='Output', description='', value=desc.Node.internalFolder)
+    ]
+
+
+def test_plugin_management():
+    """ Tests the plugin manager for registering and unregistering node.
+    """
+    # Sample Node name
+    name = SampleNode.__name__
+
+    # Register the node
+    registerNodeType(SampleNode)
+
+    # Since the Node Plugin Manager is a singleton instance
+    # We should still be able to instantiate and have a look at out registered plugins directly
+    pluginManager = _plugins.NodePluginManager()
+
+    # Assert that the plugin we have registered above is indeed registered
+    assert pluginManager.registered(name)
+
+    # Assert that the plugin can only be registered once
+    assert not pluginManager.registerNode(SampleNode)
+
+    # And once un-registered, it should no longer be present in the pluginManager
+    unregisterNodeType(SampleNode)
+
+    # Assert that the plugin we have registered above is indeed registered
+    assert not pluginManager.registered(name)
+    assert name not in pluginManager.descriptors
+
+def test_descriptor():
+    """ Tests the Descriptor and NodeDescriptor instances.
+    """
+    # Register the node
+    registerNodeType(SampleNode)
+
+    # Since the Node Plugin Manager is a singleton instance
+    # We should still be able to instantiate and have a look at out registered plugins directly
+    pluginManager = _plugins.NodePluginManager()
+
+    # Assert the descriptor is same as the Plugin NodeType
+    assert pluginManager.descriptor(SampleNode.__name__).__name__ == SampleNode.__name__
+
+    # Assert that the category of the NodeDescriptor is correct for the registered plugin
+    assert pluginManager.descriptors.get(SampleNode.__name__).category == "Sample"
+
+    # Finally unregister the plugin
+    unregisterNodeType(SampleNode)