How to use REST Assured to upload a file?
<p>I wrote a service which can upload a file to the server, and now I'm writing it's integration test with REST Assured. The functional code is as following:</p>

<pre><code>    /* Upload a new document */
    @RequestMapping(method = RequestMethod.POST)
    public ResponseEntity uploadDocument(@RequestPart("file") final MultipartFile file, final HttpServletRequest request) throws IOException {
        final String id = documentService.saveDocument(file);
        final String url = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + "/documents/" + id;
        return ControllerUtil.resourceCreatedMessage(id, url);
    }
</code></pre>

<p>To use this service, I always upload a file in Postman, and I didn't add "Content-Type = multipart/form-data" in the Headers, it works perfectly:
<a href="https://i.stack.imgur.com/IjO34.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IjO34.png" alt="enter image description here"></a></p>

<p>If I add the header info "Content-Type = multipart/form-data", I will get the message that "400 - Request is not a multipart request, see details for more information". This part also confused me because in the upper image you can see I'm sending a file in "form-data", how could it not be a multipart request? </p>

<p>Anyway, I am writing the integration test:</p>

<pre><code>@Test
public void testDocuments() throws URISyntaxException {
    // Test post a document.
    given().multiPart("file", new File(LOCATE_TO_THE_TEST_HTML_FILE))
            .expect().statusCode(201).when()
            .post(HOST + "/documents");
}
</code></pre>

<p>but I got the 415 error:</p>

<pre><code>java.lang.AssertionError: 1 expectation failed.
Expected status code &lt;201&gt; doesn't match actual status code &lt;415&gt;.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:83)
at org.codehaus.groovy.reflection.CachedConstructor.doConstructorInvoke(CachedConstructor.java:77)
at org.codehaus.groovy.runtime.callsite.ConstructorSite$ConstructorSiteNoUnwrap.callConstructor(ConstructorSite.java:84)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallConstructor(CallSiteArray.java:60)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:235)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:247)
at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:451)
at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure$validate$1.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at io.restassured.internal.RequestSpecificationImpl.applyPathParamsAndSendRequest(RequestSpecificationImpl.groovy:1632)
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.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1024)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:812)
at io.restassured.internal.RequestSpecificationImpl.invokeMethod(RequestSpecificationImpl.groovy)
at org.codehaus.groovy.runtime.callsite.PogoInterceptableSite.call(PogoInterceptableSite.java:48)
at org.codehaus.groovy.runtime.callsite.PogoInterceptableSite.callCurrent(PogoInterceptableSite.java:58)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:52)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:154)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:182)
at io.restassured.internal.RequestSpecificationImpl.applyPathParamsAndSendRequest(RequestSpecificationImpl.groovy:1637)
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.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1024)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:812)
at io.restassured.internal.RequestSpecificationImpl.invokeMethod(RequestSpecificationImpl.groovy)
at org.codehaus.groovy.runtime.callsite.PogoInterceptableSite.call(PogoInterceptableSite.java:48)
at org.codehaus.groovy.runtime.callsite.PogoInterceptableSite.callCurrent(PogoInterceptableSite.java:58)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:52)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:154)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:182)
at io.restassured.internal.RequestSpecificationImpl.post(RequestSpecificationImpl.groovy:170)
at io.restassured.internal.RequestSpecificationImpl.post(RequestSpecificationImpl.groovy)
at integrationTest.DocumentsIT.testDocuments(DocumentsIT.java:29)
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.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
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.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
</code></pre>

<p>I tried to add ".contentType("multipart/form-data")" but the same error occured. Can anyone help me?</p>