Soy nuevo en Junit, a continuación se muestra el código junit que estoy ejecutando.

package com.de.base.util.general;
import static org.junit.Assert.*;
import static org.mockito.Mockito.when;
import java.util.HashMap;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;
import org.powermock.api.mockito.PowerMockito;

@RunWith(MockitoJUnitRunner.class)
public class JReportUtilTest {
@InjectMocks 
ReportUtil w_res = new ReportUtil();

@Mock
CollectionUtil w_util;

@Test
public void test_removeHashedSettings() throws Exception {
    HashMap<String ,String> w_abc = new HashMap<String,String>();
    w_abc.put("abc","89");
    //CollectionUtil mock = org.mockito.Mockito.mock(CollectionUtil.class);
    //PowerMockito.mockStatic(CollectionUtil.class,w_abc);          
    when(w_util.createHashMap("abc:89", ":")).thenReturn(w_abc);
    assertEquals("abc:89:",ReportUtil.removeHashedSettings("1", "abc:89", ":"));
}
}

Aquí está mi api eliminadoHashedSettingsin ReportUtil

public static String removeHashedSettings(String key, String a_settings, String deilimiter) throws Exception
    {
        if (!(key != null && key.trim().length() > 0))
            return a_settings;
        if (!(a_settings != null && a_settings.trim().length() > 0))
            return a_settings;

        HashMap hSettings = CollectionUtil.createHashMap(a_settings, deilimiter);
        hSettings.remove(key);
        return getSettingFromHash(hSettings, deilimiter);
    }

A continuación se muestra el código para createHashMap en CollectionUtil que tengo que burlarme.

public static HashMap<String, String> createHashMap(String a_NameValStr, String a_Delim)// throws Exception
    {
        HashMap<String, String> w_KeyVal = new HashMap<String, String>();
        if (LOGGER.isInfoEnabled()) LOGGER.info("CollectionUtil:createHashMap:Hashing string: "+ a_NameValStr );

        if(a_NameValStr == null) return w_KeyVal;

            StringTokenizer w_StrTkn = new StringTokenizer(a_NameValStr, a_Delim);
            if( w_StrTkn.countTokens() == 0 || (w_StrTkn.countTokens()%2) != 0 )
            {
                LOGGER.warn("CollectionUtil:createHashMap:Invalid number of tokens to hash: "+ a_NameValStr+":"+w_StrTkn.countTokens() );
                return w_KeyVal;
            }

            while (w_StrTkn.hasMoreTokens()) w_KeyVal.put( w_StrTkn.nextToken(), w_StrTkn.nextToken());
        System.out.println(w_KeyVal);   
        return w_KeyVal;
    }

Aquí está el error que obtengo al ejecutar mi caso de prueba junit.

 org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
   Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.

    at com.de.base.util.general.JReportUtilTest.test_removeHashedSettings(JReportUtilTest.java:32)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
    at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Estoy usando mockito -all-1.10.19.jar, powermock-api-mockito-1.6.6.jar, powermock-core-1.6.6.jar, powermock-module-junit4-1.6.6.jar ¿Alguien puede ayudarme? ¿para resolver este problema?