modules/spring-mock-mvc/src/main/java/io/restassured/module/mockmvc/specification/MockMvcRequestSpecBuilder.java
public MockMvcRequestSpecBuilder addMultiPart(String controlName, String contentBody, String mimeType) {
        spec.multiPart(controlName, mimeType);
        return this;
    }
public MockMvcRequestSpecBuilder addMultiPart(String controlName, String contentBody, String mimeType) {
        spec.multiPart(controlName, mimeType);
        return this;
    }
Specify a string to send to the server using multi-part form data with a specific mime-type.

@param controlName Defines the control name of the body part. In HTML this is the attribute name of the input tag.
@param contentBody The string to send
@param mimeType    The mime-type
@return The request specification