Added shell test for cfengine format --check

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Ole Herman Schumacher Elgesem <ole.elgesem@northern.tech>

Author: olehermanse

tests/shell/004-format-check.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+set -e
+set -x
+
+# Setup: create a temp directory for test files
+tmpdir=$(mktemp -d)
+trap "rm -rf $tmpdir" EXIT
+
+write_formatted() {
+	printf 'bundle agent main\n{\n  vars:\n    "v" string => "hello";\n}\n' > "$1"
+}
+
+write_unformatted() {
+	printf 'bundle agent main { vars: "v" string => "hello"; }\n' > "$1"
+}
+
+# Case 1: format without --check on already-formatted file -> exit 0
+write_formatted "$tmpdir/good.cf"
+cfengine format "$tmpdir/good.cf"
+
+# Case 2: format without --check on unformatted file -> exit 0 (reformats it)
+write_unformatted "$tmpdir/bad.cf"
+cfengine format "$tmpdir/bad.cf"
+# Verify it was actually reformatted to the correct output
+write_formatted "$tmpdir/expected.cf"
+diff "$tmpdir/expected.cf" "$tmpdir/bad.cf"
+
+# Case 3: --check on already-formatted file -> exit 0
+write_formatted "$tmpdir/good2.cf"
+cfengine format --check "$tmpdir/good2.cf"
+
+# Case 4: --check on unformatted file -> exit 1
+write_unformatted "$tmpdir/bad2.cf"
+cp "$tmpdir/bad2.cf" "$tmpdir/bad2_orig.cf"
+if cfengine format --check "$tmpdir/bad2.cf"; then
+	echo "FAIL: expected exit code 1 for --check on unformatted file"
+	exit 1
+fi
+# Verify the file was NOT modified
+diff "$tmpdir/bad2_orig.cf" "$tmpdir/bad2.cf"