ExampleVFFlowPage.html

<apex:page Controller="FlowRedirectController">
	<flow:interview name="RedirectFlow" interview="{!redirectTo}" finishLocation="{!finishLocation}" >
		<!-- This Parameter is *required!* -->
		<apex:param name="StartFlow" value="YOUR_FLOW_NAME_HERE" />
		<!-- 
		Any Params you need to pass into your flow.
		<apex:param name="CaseId" value="{!CaseId}"/> 
		-->
	</flow:interview>
</apex:page>

FlowRedirectController.cls.java

Public class FlowRedirectController{
	Public Flow.Interview.RedirectFlow redirectTo {get; set;}

	public FlowRedirectController() {
	    Map<String, Object> forTestingPurposes = new Map<String, Object>();
	    forTestingPurposes.put('vFinishLocation','codefriar.wordpress.com/');
	    redirectTo = new Flow.Interview.RedirectFlow(forTestingPurposes);
	}

	Public PageReference getFinishLocation(){
	  	String finishLocation;
		if(redirectTo != null) {
			finishLocation = (string) redirectTo.getVariableValue('vFinishLocation');
		}
		PageReference send = new PageReference('/' + finishLocation);
		send.setRedirect(true);
		return send;
	}
}

Test_FlowRedirectController.cls.java

@isTest
private class Test_FlowRedirectController{

	static testmethod void SetVariablesTests() {
		PageReference pageRef = Page.ExampleVFFlow;
		Test.setCurrentPage(pageRef);
		FlowRedirectController testCtrl = new FlowRedirectController();
		System.assertEquals(testCtrl.getFinishLocation().getUrl(), '/codefriar.wordpress.com/');
	}
}