check example input causes some error in update-checks-doc tool

Author: rhysd

scripts/update-checks-doc/main.go

@@ -64,9 +64,13 @@ func Actionlint(src []byte) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	if _, err := l.Lint("test.yaml", src, p); err != nil {
+	errs, err := l.Lint("test.yaml", src, p)
+	if err != nil {
 		return nil, err
 	}
+	if len(errs) == 0 {
+		return nil, errors.New("the input example caused no error")
+	}
 
 	// Some error message contains absolute file paths. Replace them not to make the document depend
 	// on the current file system.

scripts/update-checks-doc/testdata/err/no_error.md

@@ -0,0 +1,22 @@
+<a id="hello"></a>
+## Hello
+
+Example input:
+
+```yaml
+on: push
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hello
+```
+
+Output:
+
+```
+```
+
+[Playground](https://rhysd.github.io/actionlint/#THIS_URL_WILL_BE_UPDATED)
+
+The example input does not cause any error.