public static String pluginPathJoined() {
        return pluginPath().stream().map(Path::toString).collect(Collectors.joining(","));
    }
Assemble a default plugin path containing all TestPlugin instances which are not hidden by default.
@return A list of plugin jar filenames
@throws AssertionError if any plugin failed to load, or no plugins were loaded.
connect/runtime/src/test/java/org/apache/kafka/connect/runtime/isolation/TestPlugins.java