[SalesForce] How to get parameter value from event

I have the following codes:

Event

<aura:event access="global" type="COMPONENT" description="Event template" >
<aura:attribute name="data" type="String"/>
<aura:attribute name="sample"   type="String"/>
</aura:event>

testcomp:

<aura:component >
<aura:handler name="TEST_Event" event="c:testevent" action="{!c.handleComponentEvent}"/>
<aura:attribute name="dataValue" type="String" default="testselect"/>
<aura:attribute name="sampl" type="String" />

<aura:if isTrue="{!v.dataValue == 'testselect'}">
        <c:testselect/>
</aura:if>
<aura:if isTrue="{!v.dataValue == 'testcomp2'}">
        <c:testcomp2 testdata="{!v.sampl}"/>
</aura:if>
</aura:component>

testcomp controller js:

({
handleComponentEvent : function(component, event) {
    var cmpdata = event.getParam("data");
    component.set("v.dataValue", cmpdata);

    var cmpmm = event.getParam("sample");
    component.set("v.sampl", cmpmm);

    console.log('dataValue '+component.get("v.dataValue"));
    console.log('msg '+component.get("v.sampl"));
}
})

testselect:

<aura:component >
<aura:registerEvent name="TEST_Event" type="c:testevent"/>
<table class="slds-table slds-table_cell-buffer slds-table_bordered">
    <thead>
        <tr ><th ><div >Sample Table</div></th></tr>
    </thead>
    <tbody><tr class="slds-hint-parent"><th  data-label="Batch Donation Form Name" scope="row">
                    <div class="slds-truncate" ><a aura:id="sampleId" data-value="id12345" onclick="{!c.gotoNext}">message 1</a></div>
                </th>
           </tr>
    </tbody>
</table>
</aura:component>

testselect controller js:

({
gotoNext:function(component, event, helper){
var trId = event.currentTarget.dataset.value;
console.log('trId '+trId);
var nextpage = "testcomp2";
var cmpEvent = component.getEvent("TEST_Event");
cmpEvent.setParams({
    "data" : nextpage,
    "sample" : trId});
cmpEvent.fire();
}})

testcomp2:

<aura:component >
<aura:registerEvent name="TEST_Event" type="c:testevent"/>
<aura:attribute name="testdata" type="String" />
<label>Output data here: {!v.testdata}</label>

<aura:handler name="init" action="{!c.doInit}" value="{!this}" />
</aura:component>

testcomp2 controller js:

({
doInit : function(component, event, helper) {
   var sid = event.getParam("sample");
   component.set("v.testdata",sid);
   console.log('testdata '+component.get("v.testdata"));
}})

it worked well and the sample value is displayed but when I get the value – component.get("v.testdata"), it gets an undefined value. I'm supposed to use it for my query but I didnt get any value though it displays in the page. what might went wrong?