Populating Map Document Properties under a Folder

I wrote this script that populates some of the properties for MXDs.

mxd = arcpy.mapping.MapDocument(r"C:\test\test1.mxd")
mxd = arcpy.mapping.MapDocument(r"C:\test\test2.mxd")
mxd = arcpy.mapping.MapDocument(r"C:\test\test3.mxd")
mxd.author = "Test GIS Author"
mxd.title = "Test GIS Title"
mxd.credits = "GIS Credits"
mxd.save()
del mxd

However, what I really want to accomplish is for a script to automatically populate the properties for each MXD under C:\test directory without having to declare each one of the paths for the MXDs individually. I tried working with ListFiles and using various arrays, no success yet. Can someone direct me to achieve this task ?