What exactly have you done?
Check if C:\Users\angus\.julia already exists and if you can write and change files inside. Perhaps you just lost the rights to this folder.
If it exists, juts try to rename the folder .julia to e.g. .juliaXXX and try again to add HypothesisTests from a newly started REPL.
If this works you can remove the newly created folder .julia and rename back .juliaXXX to .julia. Give full access to this folder and recursively to all its content to user angus (I hope you know how to to that). This should solve your issue.
It should also be save to just delete the folder C:\\Users\\angus\\.julia\\registries\\General. It should be regenerated in the next new REPL if you do add something.