Mock Android TextUtils static method

DummyAndroidTextUtilsMockTest.java

import android.text.TextUtils;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static junit.framework.Assert.assertTrue;
import static org.junit.Assert.assertFalse;
import static org.mockito.Matchers.any;
import static org.powermock.api.mockito.PowerMockito.mockStatic;
import static org.powermock.api.mockito.PowerMockito.when;

@RunWith(PowerMockRunner.class)
@PrepareForTest(TextUtils.class)
public class DummyAndroidTextUtilsMockTest {

    private class DummyClass {
        String a;
        String b;

        private DummyClass(String a, String b) {
            this.a = a;
            this.b = b;
        }

        public boolean bothEquals() {
            return TextUtils.equals(a, b);
        }
    }

    @Before
    public void setUp() throws Exception {
        mockStatic(TextUtils.class);

        when(TextUtils.equals(any(CharSequence.class), any(CharSequence.class))).thenAnswer(new Answer<Object>() {
            @Override
            public Object answer(InvocationOnMock invocation) throws Throwable {
                CharSequence a = (CharSequence) invocation.getArguments()[0];
                CharSequence b = (CharSequence) invocation.getArguments()[1];
                if (a == b) return true;
                int length;
                if (a != null && b != null && (length = a.length()) == b.length()) {
                    if (a instanceof String && b instanceof String) {
                        return a.equals(b);
                    } else {
                        for (int i = 0; i < length; i++) {
                            if (a.charAt(i) != b.charAt(i)) return false;
                        }
                        return true;
                    }
                }
                return false;
            }
        });
    }

    @Test
    public void testCase() throws Exception {
        assertTrue(new DummyClass("test", "test").bothEquals());
        assertFalse(new DummyClass("test", "false").bothEquals());
    }
}

Getting a java.lang.NoClassDefFoundError: org/mockito/cglib/proxy/Enhancer when running this.
What wrong could I be doing?