First, run phpwebhosting/test.php.  If you get ANY errors, PLEASE report them.  You should wait until those errors have been fixed before preceeding with the rest of the tests.

Upload these types of files and check the size/MIME-type/history for each:
empty file
normal sized file
large file
file with special characters in name (address@hidden&*()-_=+/|[{]};:'\",<.>?)
file with special characters in text
with comments
with comments that contain special characters

Create a directory
Create a directory with special characters

Upload files into each directory

Edit the files.  Preview and save each
Rename each file.  Try to put / \ ' " < > & in the name
Edit the comments.  Try to put / \ < > in the comment
Download the files
Copy the files into the other directories
Move the files into the other directories
Delete the files

Make sure you're in at least one group and that that group has access to phpwebhosting
Go up to /home
Enter a group's directory
Repeat above steps for the group's directory
Move/copy files from/to group directory.  Check the owner and history after each operation
Create two files with the same name but different content.  Move/copy one to the other and check the information/history is right

Create a file and directory by hand in the file system.  Use the Update button and check the information is correct

Test ACL support:
READ=read
ADD=upload (or copy to or move to when destination file doesn't exist)
EDIT=edit (or copy to or move to when destination file does exist)
DELETE=delete
PRIVATE=none

Test different preferences, viewing in a new window, on server, etc.