test: coverage for emitExperimentalWarning

PR-URL: https://github.com/nodejs/node/pull/17635
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-util-emit-experimental-warning.js

@@ -0,0 +1,17 @@
+'use strict';
+// Flags: --expose-internals
+const common = require('../common');
+const assert = require('assert');
+const { emitExperimentalWarning } = require('internal/util');
+
+// This test ensures that the emitExperimentalWarning in internal/util emits a
+// warning when passed an unsupported feature and that it simply returns
+// when passed the same feature multiple times.
+
+process.on('warning', common.mustCall((warning) => {
+  assert(/is an experimental feature/.test(warning.message));
+}, 2));
+
+emitExperimentalWarning('feature1');
+emitExperimentalWarning('feature1'); // should not warn
+emitExperimentalWarning('feature2');