Spring Boot Mock REST API Integration Test: look for null value in JSON response

Question

As part of my JHipster-generated Spring Boot app, I'm trying to adapt an integration test to ensure that the return JSON object contains null for a particular property:

import static org.springframework.test.web.servlet.ResultActions.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

.andExpect(jsonPath("$.selectedChannels[0].channelValue")
    .doesNotExist())

This doesn't seem to work. For the response:

{
    "selectedChannels": [{
        "name": "test channel",
        "channelValue": null
    }]
}

I would get a response:

java.lang.AssertionError: Expected no value at JSON path "$.selectedChannels[0].channelValue" but found: [null]

I suppose the "doesNotExist" call is trying to make sure that the key does not exist. I tried using "value" as well with a null value but this just throws a NPE. How do I perform this assertion successfully?

Tom · Accepted Answer · 2017-11-21 15:48:18Z

1

The JSON Path Matcher doesNotExist() is intented to be used to assert that no key is present. For your example the key channelValue is present and therefore the assertion fails. See also official Javadocs (https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/test/web/servlet/result/JsonPathResultMatchers.html#doesNotExist--) for JsonPathResultMatchers doesNotExist():

Evaluate the JSON path expression against the response content and assert that a value does not exist at the given path.

What you want for your provided response is checking if the response contains a null value for the key channelValue:

resultActions.andExpect(jsonPath("$.selectedChannels[0].channelValue").value(nullValue());

Make sure to add a static import for Hamcrest nullValue() matcher: import static org.hamcrest.Matchers.nullValue;

edited Nov 21, 2017 at 15:48

answered Nov 20, 2017 at 20:19

Tom

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3 Comments

IcedDante Over a year ago

I don't see a static method for nullValue mentioned in any of the libraries I have referenced. Can you direct me to its proper location?

Tom Over a year ago

It is a Hamcrest matcher with should already part of your JHipster applicatio. Import with import static org.hamcrest.Matchers.nullValue;

IcedDante Over a year ago

Ah, that particular matcher does not work: org.hamcrest.core.IsNull.nullValue() returns the response: Expected: null but: was <[null]>. Spring's JsonPathResultMatchers is casting null to a list of null for some reason.

IcedDante · Accepted Answer · 2017-11-21 18:14:25Z

I believe there may be some bug that causes Spring Framework (Spring Boot version 1.5.4 currently) to render the null value as a net.minidev.json.JSONArray with a single value of null. So "channelValue": null is rendered to "channelValue": [null]. This prevents the nullValue matcher from working.

Currently the only solution I could muster to this problem was to implement and use my own Matcher. Using the NullValue matcher as a template I have this:

import org.hamcrest.BaseMatcher;
import org.hamcrest.Description;
import org.hamcrest.Matcher;
import net.minidev.json.JSONArray;

/**
 * Matcher that can be used to detect if a value is null or refers to an empty list,
 * or a list that contains a single null value. 
 *
 * @param <T>
 */
public class IsNullOrEmpty<T> extends BaseMatcher<T> {

    @Override
    public boolean matches(Object item) {
        System.out.println(item.getClass().getPackage());
        if(item instanceof JSONArray) {
            JSONArray arr = ((JSONArray)item);
            return arr==null || arr.size()==0 || (arr.size()==1 && arr.get(0)==null);
        }
        return item==null;
    }

    @Override
    public void describeTo(Description description) {
        description.appendText("null or list of null");
    }

    /**
     * Detect if the value is null or contains an empty array, or an array of a single element
     * of null
     * @return
     */
    public static Matcher<Object> isNullOrEmpty() {
        return new IsNullOrEmpty<>();
    }

}

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