JSONAssert How to unit test JSON data

In Java, we can use JSONAssert to unit test JSON data easily.

1. Maven

	<dependency>
		<groupId>org.skyscreamer</groupId>
		<artifactId>jsonassert</artifactId>
		<version>1.5.0</version>
	</dependency>

2. JSON Object

To test the JSON Object, Strict or not, fields order does not matter. If the extended fields are matter, enable the strict mode.

2.1 When the strictMode is off.

	JSONObject actual = new JSONObject();
	actual.put("id", 1);
	actual.put("name", "mkyong");
	actual.put("age", 37);
	JSONAssert.assertEquals("{id:1}", actual, false); 					//Pass, extended fields doesn't matter
	JSONAssert.assertEquals("{name:\"mkyong\"}", actual, false);		//Pass
	JSONAssert.assertEquals("{name:\"mkyong\", age:37}", actual, false);//Pass
	JSONAssert.assertEquals("{name:mkyong, id:1}", actual, false);		//Pass
	JSONAssert.assertEquals("{id:1, age:37}", actual, false);			//Pass

2.2 When the strictMode is on.

	String actual = "{\"name\":\"mkyong\",\"id\":1,\"age\":37}";
	JSONAssert.assertEquals("{id:1, name:\"mkyong\", age:37}", actual, true); //Pass, fields order doesn't matter
	JSONAssert.assertEquals("{age:37, id:1, name:\"mkyong\"}", actual, true); //Pass
	JSONAssert.assertEquals("{name:\"mkyong\"}", actual, true); 		// Fail, extended fields must match
	JSONAssert.assertEquals("{name:\"mkyong\", age:37}", actual, true); // Fail, extended fields must match

3. JSON Array

To test the JSON Array, Strict or not, extended fields must match. If the fields order is matter, enable the strict mode.

3.1 When the strictMode is off.

	String result = "[1,2,3,4,5]";
	JSONAssert.assertEquals("[1,2,3,4,5]", result, false); // Pass
	JSONAssert.assertEquals("[5,3,2,1,4]", result, false); // Pass, fields order doesn't matter
	JSONAssert.assertEquals("[1,2,3,4]", result, false);   // Fail, extended fields must match

3.2 When the strictMode is on.

	String result = "[1,2,3,4,5]";
	JSONAssert.assertEquals("[1,2,3,4,5]", result, true); // Pass
	JSONAssert.assertEquals("[5,3,2,1,4]", result, true); // Fail, fields order must match.
	JSONAssert.assertEquals("[1,2,3,4]", result, true);   // Fail, extended fields must match

4. Spring Boot + JSONAssert

4.1 For Spring Boot, the JSONAssert is bundled in spring-boot-starter-test

+- org.springframework.boot:spring-boot-starter-test:jar:2.1.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test:jar:2.1.2.RELEASE:test
[INFO] |  +- org.springframework.boot:spring-boot-test-autoconfigure:jar:2.1.2.RELEASE:test
[INFO] |  +- com.jayway.jsonpath:json-path:jar:2.4.0:test
[INFO] |  |  \- net.minidev:json-smart:jar:2.3:test
[INFO] |  |     \- net.minidev:accessors-smart:jar:1.2:test
[INFO] |  |        \- org.ow2.asm:asm:jar:5.0.4:test
[INFO] |  +- junit:junit:jar:4.12:test
[INFO] |  +- org.assertj:assertj-core:jar:3.11.1:test
[INFO] |  +- org.mockito:mockito-core:jar:2.23.4:test
[INFO] |  |  +- net.bytebuddy:byte-buddy-agent:jar:1.9.7:test
[INFO] |  |  \- org.objenesis:objenesis:jar:2.6:test
[INFO] |  +- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] |  +- org.hamcrest:hamcrest-library:jar:1.3:test
[INFO] |  +- org.skyscreamer:jsonassert:jar:1.5.0:test     <<-------- JSONAssert
[INFO] |  |  \- com.vaadin.external.google:android-json:jar:0.0.20131108.vaadin1:test
[INFO] |  \- org.xmlunit:xmlunit-core:jar:2.6.2:test

4.2 A simple Spring boot integration test with JSONAssert

package com.mkyong;
import org.json.JSONException;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.skyscreamer.jsonassert.JSONAssert;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.*;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.junit4.SpringRunner;
import static org.junit.Assert.assertEquals;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) // for restTemplate
@ActiveProfiles("test")
public class BookControllerRestTemplateTest {
    private static final ObjectMapper om = new ObjectMapper();
    @Autowired
    private TestRestTemplate restTemplate;
    @MockBean
    private BookRepository mockRepository;
    /*
            "timestamp":"2019-03-05T09:34:13.207+0000",
            "status":400,
            "errors":["Author is not allowed."]
     */
    @Test
    public void save_invalidAuthor_400() throws JSONException {
        String bookInJson = "{\"name\":\" Spring REST tutorials\", \"author\":\"abc\",\"price\":\"9.99\"}";
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        HttpEntity<String> entity = new HttpEntity<>(bookInJson, headers);
        //Try exchange
        ResponseEntity<String> response = restTemplate.exchange("/books", HttpMethod.POST, entity, String.class);
        String expectedJson = "{\"status\":400,\"errors\":[\"Author is not allowed.\"]}";
        assertEquals(HttpStatus.BAD_REQUEST, response.getStatusCode());
        JSONAssert.assertEquals(expectedJson, response.getBody(), false);
        verify(mockRepository, times(0)).save(any(Book.class));

P.S Tested with Spring Boot 2