Using 7-Zip, you can select multiple RAR or other archives and select Test in the 7-Zip File Manager to test the integrity of all of them.
Alternatively, you can enable 7-Zip's shell integration feature1, use Windows Search to find all of the RAR archives (in Windows 7, use the search string type:rar), then select all of the results of the search, right-click on the results, and under 7-Zip, select Test archive.
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