Fix #823 - Write Windows files with CRLF

test/test_writefile_function.vader

@@ -0,0 +1,48 @@
+Before:
+  call ale#test#SetDirectory('/testplugin/test')
+
+After:
+  noautocmd :e! ++ff=unix
+  setlocal buftype=nofile
+
+  if filereadable('.newline-test')
+    call delete('.newline-test')
+  endif
+
+  call ale#test#RestoreDirectory()
+
+Given(A file with Windows line ending characters):
+  first
+  second
+  third
+
+Execute(Carriage returns should be included for ale#util#Writefile):
+  call ale#test#SetFilename('.newline-test')
+
+  setlocal buftype=
+  noautocmd :w
+  noautocmd :e! ++ff=dos
+
+  call ale#util#Writefile(bufnr(''), getline(1, '$'), '.newline-test')
+
+  AssertEqual
+  \ ["first\r", "second\r", "third\r", ''],
+  \ readfile('.newline-test', 'b')
+  \
+Given(A file with Unix line ending characters):
+  first
+  second
+  third
+
+Execute(Unix file lines should be written as normal):
+  call ale#test#SetFilename('.newline-test')
+
+  setlocal buftype=
+  noautocmd :w
+  noautocmd :e! ++ff=unix
+
+  call ale#util#Writefile(bufnr(''), getline(1, '$'), '.newline-test')
+
+  AssertEqual
+  \ ['first', 'second', 'third', ''],
+  \ readfile('.newline-test', 'b')