### Question:
StaxUnmarshallerContext { public String getHeader(String header) { if (headers == null) return null; return headers.get(header); } StaxUnmarshallerContext(XmlPullParser xpp);  StaxUnmarshallerContext(XmlPullParser xpp, Map<String, String> headers); String getHeader(String header); String readText(); int getCurrentDepth(); boolean testExpression(String expression); boolean testExpression(String expression, int startingStackDepth); boolean isStartOfDocument(); int nextEvent(); Map<String, String> getMetadata(); void registerMetadataExpression(String expression, int targetDepth, String storageKey); @SuppressWarnings("checkstyle:visibilitymodifier")
    final Deque<String> stack; }### Answer:
@Test public void testHeader() throws Exception { Map<String, String> headers = new HashMap<String, String>(); headers.put("key", "value"); context = getContext("", headers); assertNull("non existing key", context.getHeader("invalid key")); assertEquals("header value", "value", context.getHeader("key")); }