test: check inspect array with empty string key

PR-URL: #15258
Refs: #15159
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-util-inspect.js

@@ -959,6 +959,12 @@ if (typeof Symbol !== 'undefined') {
   assert.strictEqual(util.inspect(x), '{}');
 }
 
+{
+  const x = [];
+  x[''] = 1;
+  assert.strictEqual(util.inspect(x), '[ \'\': 1 ]');
+}
+
 // The following maxArrayLength tests were introduced after v6.0.0 was released.
 // Do not backport to v5/v4 unless all of
 // https://github.com/nodejs/node/pull/6334 is backported.