java.lang.AssertionError: Content type expected: but was: in Junit test case Spring Boot

We often see “Content type expected” error in unit test when testing spring boot MVC application. Spring boot test case makes a call to a web service.The Web service comes back with a response body. In response the test case expects content to be the same format.

In Spring Boot, if the content type of the response differs from expected content type in the Junit test case, the test case will fail by throwing an Assertion Exception. The exception shows that the expected content type differs from the actual content type.

java.lang.AssertionError: Content type expected:<application/xml> but was:<application/json>
	at org.springframework.test.util.AssertionErrors.fail(AssertionErrors.java:59)
	at org.springframework.test.util.AssertionErrors.assertEquals(AssertionErrors.java:98)
	at org.springframework.test.web.servlet.result.ContentResultMatchers.lambda$contentType$0(ContentResultMatchers.java:84)
	at org.springframework.test.web.servlet.MockMvc$1.andExpect(MockMvc.java:196)
	at com.test.StudentTestController.testStudent(StudentTestController.java:37)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
	at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
	at org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:40)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
	at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
	at java.util.Iterator.forEachRemaining(Iterator.java:116)
	at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
	at org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)
	at org.junit.vintage.engine.VintageTestEngine.execute(VintageTestEngine.java:71)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)
	at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)
	at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:137)
	at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)


Root Cause

The spring boot controller is configured either as a rest controller or as a generic controller. The response from the controller is identified with a MIME type specified in the response header. The spring boot controller returns a response that has a different content type expected in the Junit test case. The response content type may be incorrect or the expected content type may be incorrect in the Junit test case.



How to reproduce this issue

The receiver program expects a MIME content type that is different from the content type of the sender. So there is a disparity in the type of content. In the Junit test case, validate with different content type compared to the response content type of the Spring Boot MVC Controller. The Junit test case fails with this exception while comparing the type of content.

package com.yawintutor;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestController {

	@RequestMapping(value = "/student", method = RequestMethod.GET)
	public Student testPage() {
		Student st = new Student();
		st.setName("student1");
		st.setStudentId("1");
		st.setAge(30);

		return st;
	}
}
package com.yawintutor;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
import org.springframework.web.context.WebApplicationContext;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentTestController{
	@Autowired
	private WebApplicationContext webApplicationContext;
	
	private MockMvc mockMvc;
	
	@Before
	public void setup() {
		mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
	}
	
	@Test
	public void testStudent() throws Exception {
		mockMvc.perform(get("/student"))
				.andExpect(status().isOk())
				.andExpect(content().contentType("application/xml"))
				.andExpect(jsonPath("$.studentId").value("1"))
				.andExpect(jsonPath("$.name1").value("student1"))
				.andExpect(jsonPath("$.age").value(30));
	}
}


Solution 1

Check the Junit test case that the expected content type should be the same as the response content type. Change the type of content as the type of response content. In the example below content type is changed as “”application/json””.

package com.test;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
import org.springframework.web.context.WebApplicationContext;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentTestController{
	@Autowired
	private WebApplicationContext webApplicationContext;
	
	private MockMvc mockMvc;
	
	@Before
	public void setup() {
		mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
	}
	
	@Test
	public void testStudent() throws Exception {
		mockMvc.perform(get("/student"))
				.andExpect(status().isOk())
				.andExpect(content().contentType("application/json"))
				.andExpect(jsonPath("$.studentId").value("1"))
				.andExpect(jsonPath("$.name1").value("student1"))
				.andExpect(jsonPath("$.age").value(30));
	}
}


Solution 2

In Junit test case, add the code “.andDo(print())” and run the test case again, this will print the json response, check the content type of the response and change it accordingly. The example below shows the content type of response.

package com.test;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
import org.springframework.web.context.WebApplicationContext;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentTestController{
	@Autowired
	private WebApplicationContext webApplicationContext;
	
	private MockMvc mockMvc;
	
	@Before
	public void setup() {
		mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
	}
	
	@Test
	public void testStudent() throws Exception {
		mockMvc.perform(get("/student"))
				.andExpect(status().isOk())
				.andDo(print())
				.andExpect(content().contentType("application/xml"))
				.andExpect(jsonPath("$.studentId").value("1"))
				.andExpect(jsonPath("$.name1").value("student1"))
				.andExpect(jsonPath("$.age").value(30));
	}
}

The content type will show as a part of headers as shown below

MockHttpServletResponse:
           Status = 200
    Error message = null
          Headers = [Content-Type:"application/json"]
     Content type = application/json
             Body = {"studentId":"1","name":"student1","age":30}
    Forwarded URL = null
   Redirected URL = null
          Cookies = []



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