Execute (plug#shellescape() works without optional arguments):
  if has('unix')
    AssertEqual "''", plug#shellescape("")
    AssertEqual "'foo'\\'''", plug#shellescape("foo'")
  endif

Execute (plug#shellescape() ignores invalid optional argument):
  if has('unix')
    AssertEqual "''", plug#shellescape("", '')
    AssertEqual "'foo'\\'''", plug#shellescape("foo'", [])
  endif

Execute (plug#shellescape() depends on the shell):
  AssertEqual "'foo'\\'''", plug#shellescape("foo'", {'shell': 'sh'})
  AssertEqual '^"foo''^"', plug#shellescape("foo'", {'shell': 'cmd.exe'})
  AssertEqual "'foo'''", plug#shellescape("foo'", {'shell': 'powershell'})
  AssertEqual "'foo'''", plug#shellescape("foo'", {'shell': 'powershell.exe'})
  AssertEqual "'foo'''", plug#shellescape("foo'", {'shell': 'pwsh'})

Execute (plug#shellescape() supports non-trivial cmd.exe escaping):
  " batchfile
  AssertEqual '^"^^%%PATH^^%%^"', plug#shellescape("^%PATH^%", {
  \ 'shell': 'cmd.exe',
  \ })
  AssertEqual '^"^^%%PATH^^%%^"', plug#shellescape("^%PATH^%", {
  \ 'shell': 'cmd.exe',
  \ 'script': 1,
  \ })
  " command prompt
  AssertEqual '^"^^^%PATH^^^%^"', plug#shellescape("^%PATH^%", {
  \ 'shell': 'cmd.exe',
  \ 'script': 0,
  \ }),

Execute (plug#shellescape() supports non-trivial powershell.exe escaping):
  AssertEqual '''\"Foo\\''''\\Bar\"''', plug#shellescape('"Foo\''\Bar"', {
  \ 'shell': 'powershell',
  \ }),
  AssertEqual '''\"Foo\\''''\\Bar\"''', plug#shellescape('"Foo\''\Bar"', {
  \ 'shell': 'powershell.exe',
  \ }),