private boolean checkMapSizeAndEqualVal(final MultiValueMap<String, String> headersOrParams, final String key, final String value) {
        if (!headersOrParams.containsKey(key)) {
            return false;
        }
        if (headersOrParams.get(key).size() != 1) {
            return false;
        }
        return value.equals(headersOrParams.get(key).get(0));
    }
test MultiValueMap whether contain the key and the value.
shenyu-plugin/shenyu-plugin-request/src/test/java/org/apache/shenyu/plugin/request/RequestPluginTest.java