@Test
    public void testGetExtensionForJavaScript() throws Exception {
        MimeType mt = this.mimeTypes.forName("text/javascript");
        assertEquals(".js", mt.getExtension());
        assertEquals(List.of(".js", ".mjs"), mt.getExtensions());
    }
TIKA-2460 Test loading of custom-mimetypes.xml from sys prop.
tika-core/src/test/java/org/apache/tika/mime/MimeTypesReaderTest.java