I have seen many questions posted that are similar to mine but still havent found the answer so figured I would post my script. I want to change all the data sources found in all mxds in a location to point to one geodatabase. The mxds are currently referencing feature classes, shapefiles and rasters. I am wondering if there is an issue with the shapefiles that have now been moved to the gdb and no longer have the file extension.. even if so why wouldn't the feature classes sources change? Here is what I have, it runs, but there are no changes to the data sources that I can see.

UPDATE: I've now modified it to use lyr.ReplaceDataSource, which works it changing the data source for the first shapefile it encounters in the mxds, but it doesn't change the source for the other feature classes and rasters.

UPDATE 2: Im still struggling to find the answer here. I now am trying to use findandreplaceworkspacepaths on each mxd, and again the script runs, but the data sources don't change. I am printng out the old and new paths in the script and they are printing correctly.. so what is happening?? updated code below:

import arcpy, os
mxd_path = r'C:\GIS\Assimilate_Mxd_Data\Assimilate_Mxd_Data_TESTING\Input Mxd'
new_path = r'C:\GIS\Assimilate_Mxd_Data\Assimilate_Mxd_Data_TESTING\Output Data\test_output.gdb'
mxd_list = []

for dirpath, dirnames, filenames in os.walk(mxd_path):
    for filename in filenames:
        fullPath = os.path.join(dirpath, filename)
        basename, extension = os.path.splitext(filename)
        if extension == ".mxd":
            each_mxd = fullPath
            mxd_list.append(each_mxd)
for m in mxd_list:
    mxd = arcpy.mapping.MapDocument(m)
    for lyr in arcpy.mapping.ListLayers(mxd):
        if lyr.supports("DATASOURCE"):
            old_path = lyr.dataSource
            mxd.findAndReplaceWorkspacePaths(old_path,new_path,validate=True)
            print old_path,new_path
mxd.save()
del mxd