If you're using boot 1.4.x you need to modify the @springBootTest annotation to @SpringBootTest(classes = DataFlowServerConfiguration.class). 1.3.8 doesn't have this problem as well.
Spring Boot 1.4 changed their annotation system a little. Try using the @SpringBootApplication annotation for better results.
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java.lang.IllegalStateException: Marshaller must support the class of the marshalled object
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