Add regression test (#157)

.github/workflows/test.yml

@@ -0,0 +1,20 @@
+name: Run Test
+
+on:
+  pull_request:
+    branches:
+      - '*'
+  push:
+    branches:
+      - master
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Run test
+        run: ./run_test.sh

autoindent.vim

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+if empty($OUTPUT_FILE)
+  echom "Error: Environment variable OUTPUT_FILE is not set."
+  cquit! 1
+endif
+
+set nocompatible
+set runtimepath^=$PWD
+filetype plugin indent on
+
+syntax on
+augroup swiftIndent
+  autocmd!
+  autocmd BufRead,BufNewFile *.swift setlocal shiftwidth=4 expandtab
+augroup END
+
+" Apply autoindent, save and quit.
+function! s:RemoveWhitespaceAndReindent()
+  silent %s/^\s\+//
+  normal gg=G
+  execute 'write ' . fnameescape($OUTPUT_FILE)
+  quit!
+endfunction
+autocmd BufReadPost * call s:RemoveWhitespaceAndReindent()

run_test.sh

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+#!/bin/bash
+
+set -euo pipefail
+
+tempdir=$(mktemp -d)
+trap cleanup EXIT
+
+cleanup() {
+  rm -r "$tempdir"
+}
+
+for example_file in example/*.swift; do
+  autoindented_file="$tempdir/${example_file##*/}"
+  OUTPUT_FILE="$autoindented_file" vim -u autoindent.vim "$example_file"
+  diff -u --color=auto "$example_file" "$autoindented_file"
+done
+
+echo "test passed!"