How should I create a MuleMessage from String?

I'm doing the first sample at chapter 1 and the test fails at following. As this doesn't give any further information, I suspect it may be happening due to use of deprecated function - dispatch(String url, Object payload, Map<String, Object> messageProperties). Instead, I try to use dispatch(String url, MuleMessage message).

However, I can't figure out how I should create a MuleMessage out of String - productAsJson. Please help.

client.dispatch("http://localhost/8080/products", productAsJson, null);

org.mule.api.MessagingException: Error sending HTTP request.
	at org.mule.module.http.internal.request.DefaultHttpRequester.innerProcess(DefaultHttpRequester.java:331)
	at org.mule.module.http.internal.request.DefaultHttpRequester.processBlocking(DefaultHttpRequester.java:217)
	at org.mule.processor.AbstractNonBlockingMessageProcessor.process(AbstractNonBlockingMessageProcessor.java:43)
	at org.mule.module.http.internal.request.client.OneWayHttpRequesterAdapter.process(OneWayHttpRequesterAdapter.java:37)
	at org.mule.client.DefaultLocalMuleClient.dispatch(DefaultLocalMuleClient.java:156)
	at org.mule.client.DefaultLocalMuleClient.dispatch(DefaultLocalMuleClient.java:96)
	at product_registration.ProductRegistrationFunctionalTestCase.testCanRegisterProducts(ProductRegistrationFunctionalTestCase.java:25)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
	at org.junit.internal.runners.statements.FailOnTimeout$StatementThread.run(FailOnTimeout.java:74)
Caused by: java.net.ConnectException: Connection refused: no further information
	at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
	at sun.nio.ch.SocketChannelImpl.finishConnect(Unknown Source)
	at org.glassfish.grizzly.nio.transport.TCPNIOConnectorHandler.onConnectedAsync(TCPNIOConnectorHandler.java:210)
	at org.glassfish.grizzly.nio.transport.TCPNIOConnectorHandler$1.connected(TCPNIOConnectorHandler.java:158)
	at org.glassfish.grizzly.nio.transport.TCPNIOConnection.onConnect(TCPNIOConnection.java:258)
	at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:517)
	at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
	at org.mule.module.http.internal.request.grizzly.FlowWorkManagerIOStrategy.run0(FlowWorkManagerIOStrategy.java:134)
	at org.mule.module.http.internal.request.grizzly.FlowWorkManagerIOStrategy.executeIoEvent(FlowWorkManagerIOStrategy.java:77)
	at org.glassfish.grizzly.strategies.AbstractIOStrategy.executeIoEvent(AbstractIOStrategy.java:89)
	at org.glassfish.grizzly.nio.SelectorRunner.iterateKeyEvents(SelectorRunner.java:415)
	at org.glassfish.grizzly.nio.SelectorRunner.iterateKeys(SelectorRunner.java:384)
	at org.glassfish.grizzly.nio.SelectorRunner.doSelect(SelectorRunner.java:348)
	at org.glassfish.grizzly.nio.SelectorRunner.run(SelectorRunner.java:279)
	at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
	at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
	at java.lang.Thread.run(Unknown Source)