test: Add minimal test for Matrix

Add a few tests for the Matrix class. This is not full fledged but at
least a starter.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

test/meson.build

@@ -60,6 +60,7 @@ internal_tests = [
     {'name': 'file', 'sources': ['file.cpp']},
     {'name': 'flags', 'sources': ['flags.cpp']},
     {'name': 'hotplug-cameras', 'sources': ['hotplug-cameras.cpp']},
+    {'name': 'matrix', 'sources': ['matrix.cpp']},
     {'name': 'message', 'sources': ['message.cpp']},
     {'name': 'object', 'sources': ['object.cpp']},
     {'name': 'object-delete', 'sources': ['object-delete.cpp']},