The following test cases are missing in AppContentTest and must be added:

 - same file/directory specified multiple times:
    run "jpackage ... --app-content foo,foo"; jpackage should successfully handle this input

 - same file name with different contents in two input folders:
    create a text file foo/file.txt with the text "Hello"
    create a text file bar/file.txt with the text "Goodbye"
    run "jpackage ... --app-content foo/file.txt,bar/file.txt"; the contents of "file.txt" file in the output app image should be "Goodbye"

 - same file name, but one is a file, another is a directory:
    create an empty file foo/a
    create an empty file foo/a/b
    run "jpackage ... --app-content foo/a,bar/a"; the output app image should have "a/b" empty file.
    run "jpackage ... --app-content bar/a,foo/a"; the output app image should have "a" empty file.

- test that files supplied with --app-content can overwrite files produced by jpackage, e.g. replace the default app launcher executable with the file from --app-content

 - repeat all test cases for app image bundling